System and method for beam management

ABSTRACT

A first apparatus may send, to a base station in a first carrier frequency, a request associated with determination of a first beam used for communication between the base station and the UE. The first apparatus may communicate with the base station in a second carrier frequency based on the request associated with the determination of the first beam, the first carrier frequency being different from the second carrier frequency. A second apparatus may receive, from a base station in a first carrier frequency, a message associated with determination of a first beam used for communication between the base station and the UE. The second apparatus may communicate with the base station in a second carrier frequency based on the message associated with the determination of the first beam, the first carrier frequency being different from the second carrier frequency.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This Application is a Continuation of U.S. Non-Provisional ApplicationSer. No. 15/474,859 entitled “SYSTEM AND METHOD FOR BEAM MANAGEMENT” andfiled on Mar. 30, 2017, which claims the benefit of U.S. ProvisionalApplication Ser. No. 62/322,168, entitled “TRANSMIT REQUEST FOR BEAMTRACKING” and filed on Apr. 13, 2016, U.S. Provisional Application Ser.No. 62/329,180, entitled “TRANSMIT REQUEST FOR BEAM TRACKING” and filedon Apr. 28, 2016, U.S. Provisional Application Ser. No. 62/333,120,entitled “TRANSMIT REQUEST FOR BEAM TRACKING” and filed on May 6, 2016,U.S. Provisional Application Ser. No. 62/337,829, entitled “TRANSMITREQUEST FOR BEAM TRACKING” and filed on May 17, 2016, U.S. ProvisionalApplication Ser. No. 62/338,484, entitled “TRANSMIT REQUEST FOR BEAMTRACKING” and filed on May 18, 2016, U.S. Provisional Application Ser.No. 62/341,051, entitled “TRANSMIT REQUEST FOR BEAM TRACKING” and filedon May 24, 2016 and U.S. Provisional Application Ser. No. 62/447,386,entitled “SYSTEM AND METHOD FOR BEAM INDEX and filed on Jan. 17, 2017.The disclosures of the aforementioned provisional applications areexpressly incorporated by reference herein in their entireties.

BACKGROUND

Field

The present disclosure relates generally to communication systems, andmore particularly, to a user equipment and a base station that maycommunicate through one of more beams.

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources. Examples of suchmultiple-access technologies include code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example telecommunication standardis Long Term Evolution (LTE). LTE is a set of enhancements to theUniversal Mobile Telecommunications System (UMTS) mobile standardpromulgated by Third Generation Partnership Project (3GPP). LTE isdesigned to support mobile broadband access through improved spectralefficiency, lowered costs, and improved services using OFDMA on thedownlink, SC-FDMA on the uplink, and multiple-input multiple-output(MIMO) antenna technology. However, as the demand for mobile broadbandaccess continues to increase, there exists a need for furtherimprovements in LTE technology. These improvements may also beapplicable to other multi-access technologies and the telecommunicationstandards that employ these technologies.

An example of an improvement to LTE may include fifth generationwireless systems and mobile networks (5G). 5G is a telecommunicationsstandard that may extend beyond LTE and/or 4G standards. For example, 5Gmay offer higher capacity and, therefore, serve a larger number of usersin an area. Further, 5G may improve data consumption and data rates.

SUMMARY

The following presents a simplified summary of one or more aspects inorder to provide a basic understanding of such aspects. This summary isnot an extensive overview of all contemplated aspects, and is intendedto neither identify key or critical elements of all aspects nordelineate the scope of any or all aspects. Its sole purpose is topresent some concepts of one or more aspects in a simplified form as aprelude to the more detailed description that is presented later.

Path loss may be relatively high in millimeter wave (mmW) systems.Transmission may be directional to mitigate path loss. A base stationmay transmit one or more beam reference signals by sweeping in alldirections so that a user equipment (UE) may identify a best “coarse”beam. Further, the base station may transmit a beam refinement requestsignal so that the UE may track “fine” beams. If a “coarse” beamidentified by the UE changes, the UE may need to inform the base stationso that the base station may train one or more new “fine” beams for theUE.

In a first aspect, a first method, first apparatus, and firstcomputer-readable medium are provided. The first apparatus maycommunicate with a UE through a first active beam. The first apparatusmay determine that beam tracking is to be performed with the UE,including identifying a new beam for communication between the UE andthe first apparatus. The first apparatus may perform beam tracking withthe UE based on the determination that beam tracking is to be performed.The first apparatus may communicate with the UE through a second activebeam based on the beam tracking. In an aspect, the determination thatbeam tracking is to be performed for the UE includes determining a timeat which the UE is to transition from an inactive cycle of discontinuousreception (DRX) to an active cycle of DRX, and the performance of thebeam tracking is based on the determined time. In an aspect, theperformance of the beam tracking includes one or more of: transmittingat least one beam reference signal (BRS); receiving, from the UE, afirst indication of a first beam index based on the at least one BRS;transmitting, based on the first indication of the first beam index, atleast one beam refinement reference signal (BRRS); and receiving, basedon the at least one BRRS, a second indication of a second beam index,the second beam index corresponding to the second active beam. In anaspect, the performance of the beam tracking includes one or more of:receiving, from the UE, a request for beam tracking; transmitting, basedon the request for beam tracking, at least one BRRS; and receiving,based on the at least one BRRS, an indication of a beam index, the beamindex corresponding to the second active beam. In an aspect, thecommunication with the UE through the first active beam includes sendinga reference signal to the UE to determine if the first active beam isfailing, and the determination that beam tracking is to be initiated forthe UE includes receiving a response from the UE based on the referencesignal, and detecting a radio link failure based on the receivedresponse. In an aspect, the communication with the UE through the firstactive beam is performed with a first radio access technology (RAT), andthe response is received through a second RAT, the second RAT having alower carrier frequency than the first RAT. In an aspect, the referencesignal is one of a channel state information reference signal (CSI-RS),a cell-specific reference signal (CRS), a secondary synchronizationsignal (SSS), a mobility reference signal (MRS), a demodulationreference signal (DMRS), or a beam reference signal (BRS), and theresponse includes at least one of a channel quality information (CQI), asignal-to-interference-plus-noise ratio (SINR), a signal-to-noise radio(SNR), a received signal strength indicator (RSSI), a reference signalreceived power (RSRP), or a reference signal received quality (RSRQ). Inan aspect, the performance of the beam tracking with the UE includessending a message to the UE indicating that beam tracking is to beperformed, wherein the message is sent on a physical downlink controlchannel (PDCCH) or a physical downlink shared channel (PDSCH). In anaspect, the message is sent through downlink control information (DCI)in the PDCCH. In an aspect, the determination that beam tracking is tobe initiated for the UE includes determining an absence of communicationwith the UE through the first active beam. In an aspect, thedetermination of the absence of the communication with the UE throughthe first active beam is based on an absence of data carried on aphysical uplink control channel (PUCCH), an absence of data carried on aphysical uplink shared channel (PUSCH), or an absence ofacknowledgement/negative acknowledgement (ACK/NACK) messages from theUE.

In a second aspect, a second method, second apparatus, and secondcomputer-readable medium are provided. The second apparatus maycommunicate with a base station through a first active beam. The secondapparatus may receive a signal from the base station associated withbeam tracking, the beam tracking including identifying a new beam forcommunication between the second apparatus and the base station. Thesecond apparatus may communicate with the base station through a secondactive beam based on the signal associated with beam tracking. In anaspect, the signal includes a BRRS, and the second apparatus may send,to the base station, a beam index corresponding to the second activebeam based on the BRRS. In an aspect, the signal comprises a BRS, andthe second apparatus may send, to the base station, a beam indexcorresponding to a coarse beam. In an aspect, the second apparatus maysend, to the base station, a request to perform beam tracking based onthe signal. In an aspect, the communication with the base stationthrough the first active beam includes receiving a reference signal, andthe second apparatus may detect a radio link failure based on thereception of the reference signal and send an indication to the basestation based on the detected radio link failure. In an aspect, thereference signal is one of a CSI-RS, a CRS, an SSS, an MRS, a DMRS, or aBRS, and the indication includes at least one of a CQI, an SINR, an SNR,an RSSI, an RSRP, or a RSRQ. In an aspect, the communication with thebase station through the first active beam is performed with a firstRAT, and the indication is sent through a second RAT, the first RAThaving a higher carrier frequency than the second RAT. In an aspect, thesecond apparatus may perform beam tracking with the base station. In anaspect, the performance of the beam tracking includes one or more of:receiving, from the base station, at least one BRS; transmitting, to thebase station, a first indication of a first beam index based on the BRS;receiving at least one BRRS; and transmitting, based on the at least oneBRRS, a second indication of a second beam index. In an aspect, thesignal is received on a PDCCH or a PDSCH. In an aspect, the signal isreceived through DCI on the PDCCH.

In a third aspect, a third method, third apparatus, and thirdcomputer-readable medium are provided. The third apparatus maycommunicate with a UE through an active beam. The third apparatus maytransmit, to the UE, information indicating a periodicity at whichcontrol information is to be communicated on a control channel through acontrol-information beam. The third apparatus may communicate, with theUE, the control information on the control channel through thecontrol-information beam at the periodicity. In an aspect, the controlchannel includes a PUCCH, and the communication, with the UE, of thecontrol information on the control channel includes receiving, from theUE, the control information carried on the PUCCH through thecontrol-information beam based on the periodicity. In an aspect, thecontrol-information beam includes at least one candidate beam, the atleast one candidate beam corresponding to a beam index included in a setof candidate beam indexes maintained by the third apparatus. In anaspect, the control-information beam includes at least one wide beam,the at least one wide beam having an angle greater than that of theactive beam. In an aspect, the information indicating the periodicity istransmitted through radio resource control (RRC) signaling. In anaspect, the information indicating the periodicity is transmitted on aPDCCH. In an aspect, the information indicating the periodicity includesDCI of the PDCCH. In an aspect, the third apparatus may receive arequest to change the active beam, the request indicating a beam indexcorresponding to a second beam and change the active beam to the secondbeam corresponding to the beam index indicated by the request. In anaspect, the request indicates the beam index through at least one of acyclic shift or spreading across symbols. In an aspect, the requestindicates the beam index through at least one of a subcarrier region ora random access channel (RACH).

In a fourth aspect, a fourth method, fourth apparatus, and fourthcomputer-readable medium are provided. The fourth apparatus maycommunicate with a base station through an active beam. The fourthapparatus may receive, from the base station, information indicating aperiodicity at which control information is to be communicated on acontrol channel through a control-information beam. The fourth apparatusmay communicate, with the base station, the control information on thecontrol channel through the control-information beam at the periodicity.In an aspect, the control channel includes a PUCCH, and thecommunication of the control information on the control channel includessending, to the base station, the control information on the PUCCHthrough the control-information beam based on the periodicity. In anaspect, the control-information beam includes at least one candidatebeam, the at least one candidate beam corresponding to a beam indexincluded in a set of candidate beam indexes. In an aspect, thecontrol-information beam includes at least one wide beam, the at leastone wide beam having an angle greater than that of the active beam. Inan aspect, the information indicating the periodicity is received usingRRC signaling. In an aspect, the information indicating the periodicityis received on a PDCCH. In an aspect, the information indicating theperiodicity is indicated by DCI of the PDCCH. In an aspect, the fourthapparatus may transmit, to the base station, a request to change theactive beam, the request indicating a beam index corresponding to asecond beam, and change the active beam to the second beam correspondingto the beam index indicated by the request. In an aspect, the requestindicates the beam index through at least one of a cyclic shift orspreading across symbols. In an aspect, the request indicates the beamindex through at least one of a subcarrier region or a RACH.

In a fifth aspect, a fifth method, fifth apparatus, and fifthcomputer-readable medium are provided. The fifth apparatus may transmit,to a UE, on a control channel, one or more indications of one or morebeam indexes corresponding to one or more beams. The fifth apparatus maytransmit, to the UE, one or more reference signals through the one ormore beams corresponding to the one or more beam indexes. In an aspect,the control channel includes a PDCCH, and the one or more indicationsare included in one or more bits of a DCI message. In an aspect, thetransmission of the one or more indications of the one or more beamindexes corresponding to the one or more beams includes transmission ofone or more beam indexes associated with one or more BRSs, the one ormore BRSs transmitted during a synchronization subframe. In an aspect,the transmission of the one or more indications of the one or more beamindexes corresponding to the one or beams includes reception, from theUE, of one or more beam indexes corresponding to the one or more beams,and transmission of the one or more beam indexes corresponding to theone or more beams based on the one or more beam indexes that arereceived most recently. In an aspect, the one or more beam indexescorresponding to the one or more beams are received on a PUSCH or aPUCCH. In an aspect, the one or more beam indexes corresponding to theone or more beams are transmitted based on the one or more beam indexesreceived through the PUSCH when more than two symbols are used for thereference signal transmission. In an aspect, the one or more beamindexes associated with one or more beams are transmitted based on theone or more beam indexes received through the PUCCH when two or fewersymbols are used for the reference signal transmission. In an aspect,the one or more reference signals include at least one of a CSI-RS or aBRRS. In an aspect, the transmission of the one or more indications ofthe one or more beam indexes associated with the one or more beamsincludes transmission of the one or more beam indexes associated withthe one or more beams through which at least one of the CSI-RSs waspreviously transmitted.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe annexed drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed, and this description is intended to include all suchaspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network.

FIGS. 2A, 2B, 2C, and 2D are diagrams illustrating LTE examples of a DLframe structure, DL channels within the DL frame structure, an UL framestructure, and UL channels within the UL frame structure, respectively.

FIG. 3 is a diagram illustrating an example of a base station and userequipment (UE) in an access network.

FIGS. 4A and 4B are diagrams of a wireless communications system.

FIGS. 5A through 5G are diagrams of a wireless communications system.

FIG. 6 is a diagram of a wireless communications system.

FIG. 7 is a diagram of a wireless communications system.

FIG. 8 is a diagram of a wireless communications system.

FIGS. 9A through 9E are diagrams of a wireless communications system.

FIGS. 10A and 10B is a flowchart of a method of wireless communication.

FIGS. 11A and 11B is a flowchart of a method of wireless communication.

FIG. 12 is a flowchart of a method of wireless communication.

FIG. 13 is a flowchart of a method of wireless communication.

FIG. 14 is a flowchart of a method of wireless communication.

FIG. 15 is a flowchart of a method of wireless communication.

FIG. 16 is a flowchart of a method of wireless communication.

FIG. 17 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 18 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 19 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 20 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 21 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 22 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 23 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 24 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

FIG. 25 is a conceptual data flow diagram illustrating the data flowbetween different means/components in an exemplary apparatus.

FIG. 26 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, components, circuits,processes, algorithms, etc. (collectively referred to as “elements”).These elements may be implemented using electronic hardware, computersoftware, or any combination thereof. Whether such elements areimplemented as hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented as a “processing system” thatincludes one or more processors. Examples of processors includemicroprocessors, microcontrollers, graphics processing units (GPUs),central processing units (CPUs), application processors, digital signalprocessors (DSPs), reduced instruction set computing (RISC) processors,systems on a chip (SoC), baseband processors, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines, gatedlogic, discrete hardware circuits, and other suitable hardwareconfigured to perform the various functionality described throughoutthis disclosure. One or more processors in the processing system mayexecute software. Software shall be construed broadly to meaninstructions, instruction sets, code, code segments, program code,programs, subprograms, software components, applications, softwareapplications, software packages, routines, subroutines, objects,executables, threads of execution, procedures, functions, etc., whetherreferred to as software, firmware, middleware, microcode, hardwaredescription language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, or any combination thereof. Ifimplemented in software, the functions may be stored on or encoded asone or more instructions or code on a computer-readable medium.Computer-readable media includes computer storage media. Storage mediamay be any available media that can be accessed by a computer. By way ofexample, and not limitation, such computer-readable media can comprise arandom-access memory (RAM), a read-only memory (ROM), an electricallyerasable programmable ROM (EEPROM), optical disk storage, magnetic diskstorage, other magnetic storage devices, combinations of theaforementioned types of computer-readable media, or any other mediumthat can be used to store computer executable code in the form ofinstructions or data structures that can be accessed by a computer.

FIG. 1 is a diagram illustrating an example of a wireless communicationssystem and an access network 100. The wireless communications system(also referred to as a wireless wide area network (WWAN)) includes basestations 102, UEs 104, and an Evolved Packet Core (EPC) 160. The basestations 102 may include macro cells (high power cellular base station)and/or small cells (low power cellular base station). The macro cellsinclude base stations. The small cells include femtocells, picocells,and microcells.

The base stations 102 (collectively referred to as Evolved UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access Network(E-UTRAN)) interface with the EPC 160 through backhaul links 132 (e.g.,S1 interface). In addition to other functions, the base stations 102 mayperform one or more of the following functions: transfer of user data,radio channel ciphering and deciphering, integrity protection, headercompression, mobility control functions (e.g., handover, dualconnectivity), inter-cell interference coordination, connection setupand release, load balancing, distribution for non-access stratum (NAS)messages, NAS node selection, synchronization, radio access network(RAN) sharing, multimedia broadcast multicast service (MBMS), subscriberand equipment trace, RAN information management (RIM), paging,positioning, and delivery of warning messages. The base stations 102 maycommunicate directly or indirectly (e.g., through the EPC 160) with eachother over backhaul links 134 (e.g., X2 interface). The backhaul links134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Eachof the base stations 102 may provide communication coverage for arespective geographic coverage area 110. There may be overlappinggeographic coverage areas 110. For example, the small cell 102′ may havea coverage area 110′ that overlaps the coverage area 110 of one or moremacro base stations 102. A network that includes both small cell andmacro cells may be known as a heterogeneous network. A heterogeneousnetwork may also include Home Evolved Node Bs (eNBs) (HeNBs), which mayprovide service to a restricted group known as a closed subscriber group(CSG). The communication links 120 between the base stations 102 and theUEs 104 may include uplink (UL) (also referred to as reverse link)transmissions from a UE 104 to a base station 102 and/or downlink (DL)(also referred to as forward link) transmissions from a base station 102to a UE 104. The communication links 120 may use multiple-input andmultiple-output (MIMO) antenna technology, including spatialmultiplexing, beamforming, and/or transmit diversity. The communicationlinks may be through one or more carriers. The base stations 102/UEs 104may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100 MHz) bandwidthper carrier allocated in a carrier aggregation of up to a total of YxMHz (x component carriers) used for transmission in each direction. Thecarriers may or may not be adjacent to each other. Allocation ofcarriers may be asymmetric with respect to DL and UL (e.g., more or lesscarriers may be allocated for DL than for UL). The component carriersmay include a primary component carrier and one or more secondarycomponent carriers. A primary component carrier may be referred to as aprimary cell (PCell) and a secondary component carrier may be referredto as a secondary cell (SCell).

The wireless communications system may further include a Wi-Fi accesspoint (AP) 150 in communication with Wi-Fi stations (STAs) 152 viacommunication links 154 in a 5 GHz unlicensed frequency spectrum. Whencommunicating in an unlicensed frequency spectrum, the STAs 152/AP 150may perform a clear channel assessment (CCA) prior to communicating inorder to determine whether the channel is available.

The small cell 102′ may operate in a licensed and/or an unlicensedfrequency spectrum. When operating in an unlicensed frequency spectrum,the small cell 102′ may employ NR and use the same 5 GHz unlicensedfrequency spectrum as used by the Wi-Fi AP 150. The small cell 102′,employing NR in an unlicensed frequency spectrum, may boost coverage toand/or increase capacity of the access network.

The gNodeB (gNB) 180 may operate in millimeter wave (mmW) frequenciesand/or near mmW frequencies in communication with the UE 182. When thegNB 180 operates in mmW or near mmW frequencies, the gNB 180 may bereferred to as an mmW base station. Extremely high frequency (EHF) ispart of the RF in the electromagnetic spectrum. EHF has a range of 30GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters.Radio waves in the band may be referred to as a millimeter wave. NearmmW may extend down to a frequency of 3 GHz with a wavelength of 100millimeters. The super high frequency (SHF) band extends between 3 GHzand 30 GHz, also referred to as centimeter wave. Communications usingthe mmW/near mmW radio frequency band has extremely high path loss and ashort range. The mmW base station 180 may utilize beamforming 184 withthe UE 182 to compensate for the extremely high path loss and shortrange.

The EPC 160 may include a Mobility Management Entity (MME) 162, otherMMEs 164, a Serving Gateway 166, a Multimedia Broadcast MulticastService (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC)170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be incommunication with a Home Subscriber Server (HSS) 174. The MME 162 isthe control node that processes the signaling between the UEs 104 andthe EPC 160. Generally, the MME 162 provides bearer and connectionmanagement. All user Internet protocol (IP) packets are transferredthrough the Serving Gateway 166, which itself is connected to the PDNGateway 172. The PDN Gateway 172 provides UE IP address allocation aswell as other functions. The PDN Gateway 172 and the BM-SC 170 areconnected to the IP Services 176. The IP Services 176 may include theInternet, an intranet, an IP Multimedia Subsystem (IMS), a PS StreamingService (PSS), and/or other IP services. The BM-SC 170 may providefunctions for MBMS user service provisioning and delivery. The BM-SC 170may serve as an entry point for content provider MBMS transmission, maybe used to authorize and initiate MBMS Bearer Services within a publicland mobile network (PLMN), and may be used to schedule MBMStransmissions. The MBMS Gateway 168 may be used to distribute MBMStraffic to the base stations 102 belonging to a Multicast BroadcastSingle Frequency Network (MBSFN) area broadcasting a particular service,and may be responsible for session management (start/stop) and forcollecting eMBMS related charging information.

The base station may also be referred to as a gNB, Node B, evolved NodeB (eNB), an access point, a base transceiver station, a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (B SS), an extended service set (ES S), or some other suitableterminology. The base station 102 provides an access point to the EPC160 for a UE 104. Examples of UEs 104 include a cellular phone, a smartphone, a session initiation protocol (SIP) phone, a laptop, a personaldigital assistant (PDA), a satellite radio, a global positioning system,a multimedia device, a video device, a digital audio player (e.g., MP3player), a camera, a game console, a tablet, a smart device, a wearabledevice, or any other similar functioning device. The UE 104 may also bereferred to as a station, a mobile station, a subscriber station, amobile unit, a subscriber unit, a wireless unit, a remote unit, a mobiledevice, a wireless device, a wireless communications device, a remotedevice, a mobile subscriber station, an access terminal, a mobileterminal, a wireless terminal, a remote terminal, a handset, a useragent, a mobile client, a client, or some other suitable terminology.

Referring again to FIG. 1, in certain aspects, the base station 180 maytransmit, to a UE 182, on a control channel, one or more indications 198of one or more beam indexes corresponding to one or more beams. The basestation 180 may transmit, to the UE 182, one or more reference signalsthrough the one or more beams corresponding to the one or more beamindexes. In an aspect, the control channel includes a PDCCH, and the oneor more indications 198 are included in one or more bits of a DCImessage. In an aspect, the transmission of the one or more indications198 of the one or more beam indexes corresponding to the one or morebeams includes transmission of one or more beam indexes associated withone or more BRSs, the one or more BRSs transmitted during asynchronization subframe. In an aspect, the transmission of the one ormore indications 198 of the one or more beam indexes corresponding tothe one or beams includes reception, from the UE 182, of one or morebeam indexes corresponding to the one or more beams, and transmission ofthe one or more beam indexes corresponding to the one or more beamsbased on the one or more beam indexes that are received most recently.In an aspect, the one or more beam indexes corresponding to the one ormore beams are received on a PUSCH or a PUCCH. In an aspect, the one ormore beam indexes corresponding to the one or more beams are transmittedbased on the one or more beam indexes received through the PUSCH whenmore than two symbols are used for the reference signal transmission. Inan aspect, the one or more beam indexes associated with one or morebeams are transmitted based on the one or more beam indexes receivedthrough the PUCCH when two or fewer symbols are used for the referencesignal transmission. In an aspect, the one or more reference signalsinclude at least one of a CSI-RS or a BRRS. In an aspect, thetransmission of the one or more indications 198 of the one or more beamindexes associated with the one or more beams includes transmission ofthe one or more beam indexes associated with the one or more beamsthrough which at least one of the CSI-RSs was previously transmitted.

FIG. 2A is a diagram 200 illustrating an example of a DL framestructure. FIG. 2B is a diagram 230 illustrating an example of channelswithin the DL frame structure. FIG. 2C is a diagram 250 illustrating anexample of an UL frame structure. FIG. 2D is a diagram 280 illustratingan example of channels within the UL frame structure. Other wirelesscommunication technologies may have a different frame structure and/ordifferent channels. A frame (10 ms) may be divided into 10 equally sizedsubframes. Each subframe may include two consecutive time slots. Aresource grid may be used to represent the two time slots, each timeslot including one or more time concurrent resource blocks (RBs) (alsoreferred to as physical RBs (PRBs)). The resource grid is divided intomultiple resource elements (REs). For a normal cyclic prefix, an RBcontains 12 consecutive subcarriers in the frequency domain and 7consecutive symbols (for DL, OFDM symbols; for UL, SC-FDMA symbols) inthe time domain, for a total of 84 REs. For an extended cyclic prefix,an RB contains 12 consecutive subcarriers in the frequency domain and 6consecutive symbols in the time domain, for a total of 72 REs. Thenumber of bits carried by each RE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry DL reference (pilot)signals (DL-RS) for channel estimation at the UE. The DL-RS may includeCRS (also sometimes called common RS), UE-specific reference signals(UE-RS), and CSI-RS. FIG. 2A illustrates CRS for antenna ports 0, 1, 2,and 3 (indicated as RO, R1, R2, and R3, respectively), UE-RS for antennaport 5 (indicated as R5), and CSI-RS for antenna port 15 (indicated asR). FIG. 2B illustrates an example of various channels within a DLsubframe of a frame. The physical control format indicator channel(PCFICH) is within symbol 0 of slot 0, and carries a control formatindicator (CFI) that indicates whether the PDCCH occupies 1, 2, or 3symbols (FIG. 2B illustrates a PDCCH that occupies 3 symbols). The PDCCHcarries downlink control information (DCI) within one or more controlchannel elements (CCEs), each CCE including nine RE groups (REGs), eachREG including four consecutive REs in an OFDM symbol. A UE may beconfigured with a UE-specific enhanced PDCCH (ePDCCH) that also carriesDCI. The ePDCCH may have 2, 4, or 8 RB pairs (FIG. 2B shows two RBpairs, each subset including one RB pair). The physical hybrid automaticrepeat request (ARQ) (HARQ) indicator channel (PHICH) is also withinsymbol 0 of slot 0 and carries the HARQ indicator (HI) that indicatesHARQ ACK/NACK feedback based on the PUSCH. The primary synchronizationchannel (PSCH) may be within symbol 6 of slot 0 within subframes 0 and 5of a frame. The PSCH carries a primary synchronization signal (PSS) thatis used by a UE to determine subframe/symbol timing and a physical layeridentity. The secondary synchronization channel (SSCH) may be withinsymbol 5 of slot 0 within subframes 0 and 5 of a frame. The SSCH carriesa secondary synchronization signal (SSS) that is used by a UE todetermine a physical layer cell identity group number and radio frametiming. Based on the physical layer identity and the physical layer cellidentity group number, the UE can determine a physical cell identifier(PCI). Based on the PCI, the UE can determine the locations of theaforementioned DL-RS. The physical broadcast channel (PBCH), whichcarries a master information block (MIB), may be logically grouped withthe PSCH and SSCH to form a synchronization signal (SS) block. The MIBprovides a number of RBs in the DL system bandwidth, a PHICHconfiguration, and a system frame number (SFN). The PDSCH carries userdata, broadcast system information not transmitted through the PBCH suchas system information blocks (SIBs), and paging messages.

As illustrated in FIG. 2C, some of the REs carry DMRS for channelestimation at the base station. The UE may additionally transmitsounding reference signals (SRS) in the last symbol of a subframe. TheSRS may have a comb structure, and a UE may transmit SRS on one of thecombs. The SRS may be used by a base station for channel qualityestimation to enable frequency-dependent scheduling on the UL. FIG. 2Dillustrates an example of various channels within an UL subframe of aframe. A physical random access channel (PRACH) may be within one ormore subframes within a frame based on the PRACH configuration. ThePRACH may include six consecutive RB pairs within a subframe. The PRACHallows the UE to perform initial system access and achieve ULsynchronization. A physical uplink control channel (PUCCH) may belocated on edges of the UL system bandwidth. The PUCCH carries uplinkcontrol information (UCI), such as scheduling requests, a channelquality indicator (CQI), a precoding matrix indicator (PMI), a rankindicator (RI), and HARQ ACK/NACK feedback. The PUSCH carries data, andmay additionally be used to carry a buffer status report (BSR), a powerheadroom report (PHR), and/or UCI.

FIG. 3 is a block diagram of a base station 310 in communication with aUE 350 in an access network. In the DL, IP packets from the EPC 160 maybe provided to a controller/processor 375. The controller/processor 375implements layer 3 and layer 2 functionality. Layer 3 includes a radioresource control (RRC) layer, and layer 2 includes a packet dataconvergence protocol (PDCP) layer, a radio link control (RLC) layer, anda medium access control (MAC) layer. The controller/processor 375provides RRC layer functionality associated with broadcasting of systeminformation (e.g., MIB, SIBs), RRC connection control (e.g., RRCconnection paging, RRC connection establishment, RRC connectionmodification, and RRC connection release), inter radio access technology(RAT) mobility, and measurement configuration for UE measurementreporting; PDCP layer functionality associated with headercompression/decompression, security (ciphering, deciphering, integrityprotection, integrity verification), and handover support functions; RLClayer functionality associated with the transfer of upper layer packetdata units (PDUs), error correction through ARQ, concatenation,segmentation, and reassembly of RLC service data units (SDUs),re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto transport blocks(TBs), demultiplexing of MAC SDUs from TBs, scheduling informationreporting, error correction through HARQ, priority handling, and logicalchannel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370implement layer 1 functionality associated with various signalprocessing functions. Layer 1, which includes a physical (PHY) layer,may include error detection on the transport channels, forward errorcorrection (FEC) coding/decoding of the transport channels,interleaving, rate matching, mapping onto physical channels,modulation/demodulation of physical channels, and MIMO antennaprocessing. The TX processor 316 handles mapping to signalconstellations based on various modulation schemes (e.g., binaryphase-shift keying (BPSK), quadrature phase-shift keying (QPSK),M-phase-shift keying (M-PSK), M-quadrature amplitude modulation(M-QAM)). The coded and modulated symbols may then be split intoparallel streams. Each stream may then be mapped to an OFDM subcarrier,multiplexed with a reference signal (e.g., pilot) in the time and/orfrequency domain, and then combined together using an Inverse FastFourier Transform (IFFT) to produce a physical channel carrying a timedomain OFDM symbol stream. The OFDM stream is spatially precoded toproduce multiple spatial streams. Channel estimates from a channelestimator 374 may be used to determine the coding and modulation scheme,as well as for spatial processing. The channel estimate may be derivedfrom a reference signal and/or channel condition feedback transmitted bythe UE 350. Each spatial stream may then be provided to a differentantenna 320 via a separate transmitter 318TX. Each transmitter 318TX maymodulate an RF carrier with a respective spatial stream fortransmission.

At the UE 350, each receiver 354RX receives a signal through itsrespective antenna 352. Each receiver 354RX recovers informationmodulated onto an RF carrier and provides the information to the receive(RX) processor 356. The TX processor 368 and the RX processor 356implement layer 1 functionality associated with various signalprocessing functions. The RX processor 356 may perform spatialprocessing on the information to recover any spatial streams destinedfor the UE 350. If multiple spatial streams are destined for the UE 350,they may be combined by the RX processor 356 into a single OFDM symbolstream. The RX processor 356 then converts the OFDM symbol stream fromthe time-domain to the frequency domain using a Fast Fourier Transform(FFT). The frequency domain signal comprises a separate OFDM symbolstream for each subcarrier of the OFDM signal. The symbols on eachsubcarrier, and the reference signal, are recovered and demodulated bydetermining the most likely signal constellation points transmitted bythe base station 310. These soft decisions may be based on channelestimates computed by the channel estimator 358. The soft decisions arethen decoded and deinterleaved to recover the data and control signalsthat were originally transmitted by the base station 310 on the physicalchannel. The data and control signals are then provided to thecontroller/processor 359, which implements layer 3 and layer 2functionality.

The controller/processor 359 can be associated with a memory 360 thatstores program codes and data. The memory 360 may be referred to as acomputer-readable medium. In the UL, the controller/processor 359provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, and control signalprocessing to recover IP packets from the EPC 160. Thecontroller/processor 359 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DLtransmission by the base station 310, the controller/processor 359provides RRC layer functionality associated with system information(e.g., MIB, SIBS) acquisition, RRC connections, and measurementreporting; PDCP layer functionality associated with headercompression/decompression, and security (ciphering, deciphering,integrity protection, integrity verification); RLC layer functionalityassociated with the transfer of upper layer PDUs, error correctionthrough ARQ, concatenation, segmentation, and reassembly of RLC SDUs,re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; andMAC layer functionality associated with mapping between logical channelsand transport channels, multiplexing of MAC SDUs onto TBs,demultiplexing of MAC SDUs from TBs, scheduling information reporting,error correction through HARQ, priority handling, and logical channelprioritization.

Channel estimates derived by a channel estimator 358 from a referencesignal or feedback transmitted by the base station 310 may be used bythe TX processor 368 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 368 may be provided to different antenna352 via separate transmitters 354TX. Each transmitter 354TX may modulatean RF carrier with a respective spatial stream for transmission.

The UL transmission is processed at the base station 310 in a mannersimilar to that described in connection with the receiver function atthe UE 350. Each receiver 318RX receives a signal through its respectiveantenna 320. Each receiver 318RX recovers information modulated onto anRF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 thatstores program codes and data. The memory 376 may be referred to as acomputer-readable medium. In the UL, the controller/processor 375provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover IP packets from the UE 350. IP packets from thecontroller/processor 375 may be provided to the EPC 160. Thecontroller/processor 375 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Extremely high frequency (EHF) is part of the RF in the electromagneticspectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between1 millimeter and 10 millimeters. Radio waves in the band may be referredto as a millimeter wave. Near mmW may extend down to a frequency of 3GHz with a wavelength of 100 millimeters (the super high frequency (SHF)band extends between 3 GHz and 30 GHz, also referred to as centimeterwave). While the disclosure herein refers to mmWs, it should beunderstood that the disclosure also applies to near mmWs. Further, whilethe disclosure herein refers to mmW base stations, it should beunderstood that the disclosure also applies to near-mmW base stations.

In order to build a useful communication network in the millimeterwavelength spectrum, a beamforming technique may be used to compensatefor path loss. Beamforming technique focuses the RF energy into a narrowdirection to allow the RF beam to propagate farther in that direction.Using the beamforming technique, non-line of sight (NLOS) RFcommunication in the millimeter wavelength spectrum may rely onreflection and/or diffraction of the beams to reach the UE. If thedirection becomes blocked, either because of UE movement or changes inthe environment (e.g., obstacles, humidity, rain, etc.), the beam maynot be able to reach the UE. Thus, in order to ensure that the UE hascontinuous, seamless coverage, multiple beams in as many differentdirection as possible may be available. In an aspect, the beamformingtechnique may require that the mmW base stations and the UEs transmitand receive in a direction that allows the most RF energy to becollected.

FIGS. 4A and 4B are diagrams illustrating an example of the transmissionof beamformed signals between a base station 402 and a UE 404. The basestation 402 may be embodied as a base station in a mmW system (e.g., mmWbase station). When the UE 404 turns on, the UE 404 searches for anearby NR network. The UE 404 discovers the base station 402, whichbelongs to an NR network. The base station 402 transmits an SS blockincluding the PSS, SSS, and the PBCH (including the MIB) periodically indifferent transmit directions 402 a-402 h. The UE 404 receives thetransmission 402 e including the PSS, SSS, and PBCH. Based on thereceived SS block, the UE 404 synchronizes to the NR network and campson a cell associated with the base station 402.

Referring to FIG. 4A, diagram 400 illustrates a base station 402 of ammW system transmitting beamformed signals 406 (e.g., a BRS) indifferent transmit directions (e.g., directions A, B, C, and D). In anexample, the base station 402 may sweep through the transmit directionsaccording to a sequence A-B-C-D. In another example, the base station402 may sweep through the transmit directions according to the sequenceB-D-A-C. Although only four transmit directions and two transmitsequences are described with respect to FIG. 4A, any number of differenttransmit directions and transmit sequences are contemplated.

After transmitting the signals, the base station 402 may switch to areceive mode. In the receive mode, the base station 402 may sweepthrough different receive directions in a sequence or patterncorresponding (mapping) to a sequence or pattern in which the basestation 402 previously transmitted the synchronization/discovery signalsin the different transmit directions. For example, if the base station402 previously transmitted the synchronization/discovery signals intransmit directions according to the sequence A-B-C-D, then the basestation 402 may sweep through receive directions according to thesequence A-B-C-D in an attempt to receive an association signal from aUE 404. In another example, if the base station 402 previouslytransmitted the synchronization/discovery signals in transmit directionsaccording to the sequence B-D-A-C, then the base station 402 may sweepthrough receive directions according to the sequence B-D-A-C in anattempt to receive the association signal from the UE 404.

A propagation delay on each beamformed signal allows a UE 404 to performa receive (RX) sweep. The UE 404 in a receive mode may sweep throughdifferent receive directions in an attempt to detect asynchronization/discovery signal 406 (see FIG. 4B). One or more of thesynchronization/discovery signals 406 may be detected by the UE 404.When a strong synchronization/discovery signal 406 is detected, the UE404 may determine an optimal transmit direction of the base station 402and an optimal receive direction of the UE 404 corresponding to thestrong synchronization/discovery signal. For example, the UE 404 maydetermine preliminary antenna weights/directions of the strongsynchronization/discovery signal 406, and may further determine a timeand/or resource where the base station 402 is expected to optimallyreceive a beamformed signal. Thereafter, the UE 404 may attempt toassociate with the base station 402 via a beamformed signal.

The base station 402 may sweep through a plurality of directions using aplurality of ports in a cell-specific manner in a first symbol of asynchronization subframe. For example, the base station 402 may sweepthrough different transmit directions (e.g., directions A, B, C, and D)using four ports in a cell-specific manner in a first symbol of asynchronization subframe. In an aspect, these different transmitdirections (e.g., directions A, B, C, and D) may be considered “coarse”beam directions. In an aspect, a BRS may be transmitted in differenttransmit directions (e.g., directions A, B, C, and D).

In an aspect, the base station 402 may sweep the four different transmitdirections (e.g., directions A, B, C, and D) in a cell-specific mannerusing four ports in a second symbol of a synchronization subframe. Asynchronization beam may occur in a second symbol of the synchronizationsubframe.

Referring to diagram 420 of FIG. 4B, the UE 404 may listen forbeamformed discovery signals in different receive directions (e.g.,directions E, F, G, and H). In an example, the UE 404 may sweep throughthe receive directions according to a sequence E-F-G-H. In anotherexample, the UE 404 may sweep through the receive directions accordingto the sequence F-H-E-J. Although only four receive directions and tworeceive sequences are described with respect to FIG. 4B, any number ofdifferent receive directions and receive sequences are contemplated.

The UE 404 may attempt the association by transmitting beamformedsignals 426 (e.g., association signals or another indication of a best“coarse” beam or a best “fine” beam) in the different transmitdirections (e.g., directions E, F, G, and H). In an aspect, the UE 404may transmit an association signal 426 by transmitting along the optimalreceive direction of the UE 404 at the time/resource where the basestation 402 is expected to optimally receive the association signal. Thebase station 402 in the receive mode may sweep through different receivedirections and detect the association signal 426 from the UE 404 duringone or more timeslots corresponding to a receive direction. When astrong association signal 426 is detected, the base station 402 maydetermine an optimal transmit direction of the UE 404 and an optimalreceive direction of the base station 402 corresponding to the strongassociation signal. For example, the base station 402 may determinepreliminary antenna weights/directions of the strong association signal426, and may further determine a time and/or resource where the UE 404is expected to optimally receive a beamformed signal. Any of theprocesses discussed above with respect to FIGS. 4A and 4B may be refinedor repeated over time such that the UE 404 and base station 402eventually learn the most optimal transmit and receive directions forestablishing a link with each other. Such refinement and repetition maybe referred to as beam training.

In an aspect, the base station 402 may choose a sequence or pattern fortransmitting the synchronization/discovery signals according to a numberof beamforming directions. The base station 402 may then transmit thesignals for an amount of time long enough for the UE 404 to sweepthrough a number of beamforming directions in an attempt to detect asynchronization/discovery signal. For example, a BS beamformingdirection may be denoted by n, where n is an integer from 0 to N, Nbeing a maximum number of transmit directions. Moreover, a UEbeamforming direction may be denoted by k, where k is an integer from 0to K, K being a maximum number of receive directions. When the UE 404detects a synchronization/discovery signal from the base station 402,the UE 404 may discover that the strongest synchronization/discoverysignal is received when the UE 404 beamforming direction is k=2 and thebase station 402 beamforming direction is n=3. Accordingly, the UE 404may use the same antenna weights/directions for responding (transmittinga beamformed signal) to the base station 402 in a corresponding responsetimeslot. That is, the UE 404 may send a signal to the base station 402using UE 404 beamforming direction k=2 during a timeslot when the basestation 402 is expected to perform a receive sweep at base station 402beamforming direction n=3.

Path loss may be relatively high in mmW systems. Transmission may bedirectional to mitigate path loss. A base station may transmit one ormore beam reference signals by sweeping in all directions so that a UEmay identify a best “coarse” beam. Further, the base station maytransmit a BRRS so that the UE may track “fine” beams. In variousaspects, a CSI-RS may be used to track fine beams and, therefore,reference to BRRS may include reference to a CSI-RS. If a “coarse” beamidentified by the UE changes, the UE may need to inform the base stationso that the base station may train one or more new “fine” beams for theUE.

In various aspects, the UE may send an index of a best beam andcorresponding beam refinement reference signal session request to thebase station in a subframe reserved for a RACH. The UE may occupy one ormore tones reserved for RACH. Further, the UE may occupy tones that arereserved for scheduling request but not for RACH transmission.

FIGS. 5A through 5G are diagrams illustrating an example of thetransmission of beamformed signals between a base station and a UE. Thebase station 502 may be embodied as a base station in a mmW system (mmWbase station), such as the mmW base station 180. In one aspect, the basestation 502 may be collocated with another base station, such as an eNB,a cellular base station, or other base station (e.g., a base stationconfigured to communicate in a sub-6 GHz band). While some beams areillustrated as adjacent to one another, such an arrangement may bedifferent in different aspects (e.g., beams transmitted during a samesymbol may not be adjacent to one another). Additionally, the number ofillustrated beams is to be regarded as illustrative.

The base station 502 may include hardware for performing analog and/ordigital beamforming. If the base station 502 is equipped with analogbeamforming, at any one time, the base station 502 may transmit orreceive a signal in only one direction. If the base station 502 isequipped with digital beamforming, the base station 502 may concurrentlytransmit multiple signals in multiple directions or may receive multiplesignals concurrently in multiple directions.

Further, the UE 504, for example, may include hardware for performinganalog and/or digital beamforming. If the UE 504 is equipped with analogbeamforming, at any one time, the UE 504 may transmit or receive asignal in only one direction. If the UE 504 is equipped with digitalbeamforming, the UE 504 may concurrently transmit multiple signals inmultiple directions or may concurrently receive multiple signals inmultiple directions.

In the mmW network, UEs may perform beam sweeps with mmW base stationswithin range. For example, the base station 502 may transmit m beams ina plurality of different spatial directions. The UE 504 may listen/scanfor the beam transmissions from the base station 502 in n differentreceive spatial directions. When listening/scanning for the beamtransmissions, the UE 504 may listen/scan for the beam sweeptransmission from the base station 502 m times in each of the ndifferent receive spatial directions (a total of m*n scans). In anotheraspect, in a beam sweep, the UE 504 may transmit n beams in a pluralityof different spatial directions. The base station 502 listens/scans forthe beam transmissions from the UE 504 in m different receive spatialdirections. When listening/scanning for the beam transmissions, the basestation 502 may listen/scan for the beam sweep transmission from the UE504 n times in each of the m different receive spatial directions (atotal of m*n scans).

Based on the performed beam sweeps, the UEs and/or the mmW base stationsmay determine a channel quality associated with the performed beamsweeps. For example, the UE 504 may determine the channel qualityassociated with the performed beam sweeps. Alternatively, the basestation 502 may determine the channel quality associated with theperformed beam sweeps. If the UE 504 determines a channel qualityassociated with the performed beam sweeps, the UE 504 may send thechannel quality information (also referred to as beam sweep resultinformation) to the base station 502. The UE 504 may send the beam sweepresult information to the base station 502. If the base station 502determines a channel quality associated with the performed beam sweeps,the base station 502 may send the beam sweep result information to theUE 504. In an aspect, the channel quality may be affected by a varietyof factors. The factors include movement of the UE 504 along a path ordue to rotation (e.g., a user holding and/or rotating the UE 504),movement along a path behind obstacles, and/or movement withinparticular environmental conditions (e.g., obstacles, rain, humidity).The UE 504 and the base station 502 may also exchange other information,for example, associated with for beamforming (e.g., analog or digitalbeamforming capabilities, beamforming type, timing information,configuration information, etc.).

Based on the received information, the base station 502 and/or the UE504 may determine various configuration information, such as mmW networkaccess configuration information, information for adjusting beamsweeping periodicity, information regarding overlapping coverage forpredicting a handoff to another base station, such as a mmW basestation.

In an aspect, a beam set may contain eight different beams. For example,FIG. 5A illustrates eight beams 521, 522, 523, 524, 525, 526, 527, 528for eight directions. In aspects, the base station 502 may be configuredto beamform for transmission of at least one of the beams 521, 522, 523,524, 525, 526, 527, 528 toward the UE 504. In one aspect, the basestation 502 can sweep/transmit directions using eight ports during asubframe (e.g., synchronization subframe).

In an aspect, a base station may transmit a signal, such as a BRS, in aplurality of directions, for example, during a synchronization subframe.In one aspect, this transmission may be cell-specific. Referring to FIG.5B, the base station 502 may transmit a first set of beams 521, 523,525, 527 in four directions. For example, the base station 502 maytransmit a BRS in a synchronization subframe of each of the transmitbeams 521, 523, 525, 527.

In an aspect, these beams 521, 523, 525, 527 transmitted in the fourdirections may be odd-indexed beams 521, 523, 525, 527 for the fourdirections out of a possible eight for the beam set. For example, thebase station 502 may be capable of transmitting beams 521, 523, 525, 527in directions adjacent to other beams 522, 524, 526, 528 that the basestation 502 is configured to transmit. In an aspect, this configurationin which the base station 502 transmits beams 521, 523, 525, 527 for thefour directions may be considered a “coarse” beam set.

The UE 504 may determine a respective beam index (sometimes abbreviatedas “BI”) corresponding to a respective beam. In various aspects, thebeam index may be indicate at least a direction for communicatingthrough a corresponding beam toward the UE 504 (e.g., a beamformingdirection). For example, the beam index may be a logical beam indexassociated with an antenna port, OFDM symbol index, and/or BRStransmission period, which may be indicated by one or more bits (e.g., 9bits). For example, the UE 504 may be configured to determine a beamindex corresponding to a beam based on a time at which a BRS isreceived—e.g., a symbol or slot during which a BRS is received mayindicate a beam index corresponding to a beam.

In FIG. 5C, the UE 504 may determine or select a beam index (sometimesabbreviated as “BI”) that is strongest or preferable. For example, theUE 504 may determine that the beam 525 carrying a BRS is strongest orpreferable. The UE 504 may select a beam by measuring values for areceived power or received quality associated with each of the first setof beams 521, 523, 525, 527. In one aspect, the received power may bereferred to as a BRS received power (BRSRP).

The UE 504 may compare respective values to one another. The UE 504 mayselect a “best” beam. In an aspect, the best beam may be a beam thatcorresponds to the greatest or highest value (e.g., the best beam may bea beam with the highest BRSRP). The selected beam may correspond to abeam index, which may be a beam index with respect to the base station502. For example, the UE 504 may determine that the BRSRP correspondingto the fifth beam 525 is the highest, and therefore the fifth beam 525is the best beam as determined by the UE 504.

The UE 504 may transmit a first indication 560 of the fifth beam 525 tothe base station 502. In an aspect, the first indication 560 may includea request to transmit a BRRS. The BRRS may be UE-specific. One ofordinary skill would appreciate that the BRRS may be referred to bydifferent terminology without departing from the present disclosure,such as a beam refinement signal, a beam tracking signal, or anotherterm.

In one aspect, the base station 502 may trigger transmission of thefirst indication 560. For example, the base station 502 may triggertransmission of the first indication 560 by a DCI message.

The base station 502 may receive the first indication 560. In oneaspect, the first indication 560 may include a beam adjustment request(BAR) (e.g., a request for beam tracking, a request for a BRRS, arequest for the base station to start transmitting on an indicated beamindex without any further beam tracking, and the like). In one aspect,the BAR may be included in a MAC control element (CE). In one aspect,the first indication 560 may be indicated by a scheduling request.

In one aspect, the UE 504 may transmit a BAR once during a specificinterval, which may be defined by a timer configured through RRCsignaling (e.g., a “prohibit BAR timer”). In aspects, the UE 504 maytrigger a BAR if the prohibit BAR timer is not running and at least onecondition is satisfied. In one aspect, if the UE 504 has uplinkresources allocated for new transmission for a transmission timeinterval (TTI), the UE 504 may generate and transmit a BAR MAC CE, andstart or restart the prohibit BAR timer. In another aspect, the UE 504may be configured with a dedicated scheduling request for BRRS request.In such an aspect, the UE 504 may signal the dedicated schedulingrequest for BRRS request in a scheduling request region of a RACHsubframe (and the UE 504 may start or restart the prohibit BAR timer).In another aspect, the UE 504 may trigger a scheduling request (e.g.,when a dedicated scheduling request for BRRS request is not configuredfor the UE 504 and/or when the UE 504 lacks uplink resources allocatedfor new transmission for this TTI).

In aspects, the first indication 560 may include a beam stateinformation (BSI) report. The BSI report may include a beam index and areceived power. For example, the UE 504 may measure a BRSRPcorresponding to a beam through which a BRS is received, and the UE 504may include the BRSRP and the beam index corresponding to the beam witha “best” (e.g., highest) BRSRP. The UE 504 may transmit the firstindication 560 on PUCCH (e.g., xPUCCH) or an PUSCH (e.g., xPUSCH), forexample, as a format of uplink control information where a BSI reportconsists of a beam index and a BRSRP.

Based on the first indication 560, the base station 502 may determinethe beam index corresponding to the fifth beam 525. In FIG. 5D, the basestation 502 may transmit a second set of beams based on the firstindication 560 (e.g., based on a beam index indicated by the firstindication 560). For example, the UE 504 may indicate that a fifth beam525 is the best beam and, in response, the base station 502 may transmita second set of beams 524, 525, 526 to the UE 504 based on the indicatedbeam index. In an aspect, the beams 524, 525, 526 transmitted based onthe first indication 560 may be closer (e.g., spatially and/ordirectionally) to the fifth beam 525 than those other beams 521, 523,527 of the first set of beams.

In an aspect, the beams 524, 525, 526 transmitted based on the firstindication 560 may be considered a “fine” beam set. In an aspect, thebase station 502 may transmit a BRRS through each of the beams 524, 525,526 of the fine beam set. In an aspect, the beams 524, 525, 526 of thefine beam set may be adjacent. In an aspect, BRRS transmission can span1, 2, 5 or 10 OFDM symbols and may be associated with a BRRS resourceallocation, BRRS process indication, and/or a beam refinement processconfiguration.

Based on the BRRS transmission through the beams 524, 525, 526 of thefine beam set, the UE 504 may transmit a second indication 565 to thebase station 502 to indicate a “best” beam. In an aspect, the secondindication 565 may use two (2) bits to indicate the selected beam. Forexample, the UE 504 may transmit the second indication 565 thatindicates a beam index corresponding to the selected beam 525. In oneaspect, the second indication 565 may report beam refinement information(BRI). In one aspect, the second indication 565 may include a resourceindex (e.g., a BRRS-RI) and/or a reference power (RP) associated withthe reception of the BRRS as measured by the UE 504 (e.g., a BRRS-RP).The base station 502 may then communicate with the UE 504 through theselected beam 525.

Referring to FIG. 5E, the base station 502 may transmit a BRS in aplurality of directions during a synchronization subframe. In an aspect,the base station 502 may transmit the BRS periodically and/orcontinuously, e.g., even after the UE 504 has communicated the secondindication 565. For example, the base station 502 may transmit beams521, 523, 525, 527 that each include a BRS (e.g., a “coarse” beam set).

Referring to FIG. 5F, the quality of a selected beam 525 may deteriorateso that the UE 504. For example, when the base station 502 and the UE504 are communicating through the selected beam 525, the selected beam525 may become occluded or otherwise unsatisfactory such that the basestation 502 and the UE 504 may prefer to communicate through anotherbeam. Based on the BRS (e.g., transmitted during a synchronizationsubframe), the UE 504 may determine a new beam 523 through which tocommunicate. For example, the UE 504 may determine that the third beam523 through which a BRS is communicated may be the best beam. The UE 504may select a beam based by measuring values for a received power (e.g.,BRSRP) or received quality associated with each of the set of beams 521,523, 525, 527, comparing respective values to one another, and selectingthe beam that corresponds to the highest value. The selected beam maycorrespond to a beam index at the base station 502. The UE 504 maytransmit a third indication 570 indicating this beam index to the basestation 502. In an aspect, the third indication 570 may include arequest to transmit a BRRS. The BRRS may be UE-specific. In one aspect,a BAR may be used to request the base station 502 to transmit a BRRS. Inone aspect, the third indication 570 may be triggered by the basestation 502, such as by a DCI message. Similar to the first indication560, the third indication 570 may be included in a scheduling request.

With respect to FIG. 5G, the base station 502 may receive the thirdindication 570 from the UE 504. The base station 502 may be configuredto determine a beam index based on at least the third indication 570.The base station 502 and the UE 504 may perform a beam refinementprocedure, such as illustrated with respect to FIG. 5E (e.g., in orderto select a new beam through which to communicate).

Referring to FIG. 6, a diagram of a wireless communications system 600is illustrated. The base station 602 may be an aspect of the basestation 502, the base station 310, the base station 102, the mmW basestation 180, and/or another base station. The UE 604 may be an aspect ofthe UE 504, the UE 350, the UE 104, the UE 182, and/or another UE.

In the illustrated aspect, the base station 602 may include up to eightantenna ports for BRS transmission. In various aspects, the base station602 may send, to the UE 604, one or more BRSs 612 a-h (e.g., asdescribed with respect to FIGS. 5A-5G). Each BRS 612 a-h may becommunicated through a respective beam 620 a-h. For example, the basestation 602 may send a first BRS 612 a through the first beam 620 a withwhich the first BRS 612 a is associated. The UE 604 may track one ormore beams 620 a-h through periodically measuring a BRS 612 a-hassociated with a respective one of the beams 620 a-h. In an aspect, thetransmission period of the BRSs may be configured by an indicator on aPBCH, such as an enhanced or evolved PBCH (ePBCH). The transmissionperiod may be associated with the time to sweep the beams 620 a-hthrough which the BRSs 612 a-h are transmitted.

In aspects, the UE 604 may receive, through the set of beams 620 a-h, aset of BRSs 612 a-h. Each BRS 612 of the set of BRSs 612 a-h may beassociated with a beam index that corresponds to the beam 620 a-hthrough which the BRS 612 is sent. The UE 604 may measure a signalquality of the BRSs 612 a-h, and each measured signal quality maycorrespond to a beam 620 a-h of the set of beams. For example, the UE604 may measure the signal qualities of the third BRS 612 c, the fourthBRS 612 d, the fifth BRS 612 e, and the sixth BRS 612 f, whichrespectively correspond to the third beam 620 c, the fourth beam 620 d,the fifth beam 620 e, and the sixth beam 620 f. In aspects, the UE 604may not receive each of the BRSs 612 a-h.

In one aspect, the UE 604 may measure the signal quality as a receivedpower. In one aspect, the signal quality may correspond to a BRSRP. Forexample, the UE 604 may measure the BRSRP in decibels (dB) and/ordecibel-milliwatts (dBm). In other aspects, the UE 604 may measure thesignal quality as another value, such as a received quality (RQ), ansignal-to-interference ratio (SIR), an SINR, an SNR, an RSRP, an RSRQ,an RSSI, or another metric.

The UE 604 may transmit, to the base station 602, a first indication(e.g., the first indication 560) that indicates a beam indexcorresponding to a beam with a “best” (e.g., highest) measured signalquality (e.g., BRSRP). The first indication may be a BSI report, whichmay include a beam index and a BRSRP corresponding to a beam of the setof beams 620 a-h. For example, the UE 604 may measure a best BRSRP forthe fifth beam 620 e. The UE 604 may generate a BSI report that includesa BRSRP and a beam index corresponding to the fifth beam 620 e. The UE604 may transmit the BSI report to the base station 602 as the firstindication.

The base station 602 may transmit a BRRS 614. In aspects, the BRRSs 614c-f may not be transmitted on each beam 620 a-h. For example, the basestation 602 may transmit the BRRSs 614 c-f on a subset of beams 620 c-fof the set of beams 620 a-h. For example, the base station 602 maytransmit the BRRSs 614 c-f on the subset of beams 620 c-f that is nearor close to the beam 620 e indicated by the first indication. In anaspect, the base station 602 may transmit the beams 620 c-f as a fineset of beams for beam refinement with the UE 604.

The UE 604 may select a beam of the subset of beams 620 c-f. Forexample, the UE 604 may measure a signal quality (e.g., received power)for each BRRS 614 c-f of the set of BRRSs 614 c-f sent through thesubset of beams 620 c-f. The UE 604 may determine a best (e.g., highest)signal quality (e.g., received power) for a BRRS of the set of BRRSs 614c-f (e.g., the fifth BRRS 614 e). The UE 604 may transmit a secondindication (e.g., the second indication 565) to the base station 602,which may include a beam index corresponding to the selected beam (e.g.,a beam index corresponding to the fifth beam 620 e).

The UE 604 and the base station 602 may then communicate 640 through theselected beam corresponding the beam index indicated by the UE 604 inthe second indication. The communication 640 may be uplink and/ordownlink communication. For example, the base station 602 and the UE 604may communicate through the same or different beams for uplinkcommunication and downlink communication.

In an aspect, at least one of the base station 602 and/or the UE 604 maymaintain an set of beam indexes 630. The set of beam indexes 630 mayinclude beam indexes corresponding to beams from the base station 602and/or another transmission point (e.g., another eNB or base station),which may allow dynamic point selection and/or joint transmission frommultiple transmission points to the UE 604.

Although the UE 604 is illustrated as maintaining the set of beamindexes 630, the base station 602 may maintain a similar set of beamindexes. The base station 602 may maintain an set of beam indexes basedon information from the UE 604, such as one or more BSI reports.

The UE 604 may maintain a set of beam indexes 630 as an active set. Insuch an aspect, the UE 604 may synchronize with the base station 602based on beams in the set of beam indexes 630 (e.g., soft handover fromone beam of the beams 620 a-h to another beam of the beams 620 a-h).Beams corresponding to the beam indexes included in the set of beamindexes 630 may be used for PDCCH (e.g., xPDCCH, such as an enhancedPDCCH (ePDCCH)), PDSCH (e.g., xPDSCH, such as an enhanced PDSCH(ePDSCH)), PUCCH (e.g., xPUCCH, such as an enhanced PUCCH (ePUCCH)),and/or PUSCH (e.g., xPUSCH, such as an enhanced PUSCH (ePUSCH))communication. The base station 602 and/or the UE 604 may periodicallyand/or continuously update the set of beam indexes 630, for example,based on measurements of a BRS 612 and/or BRRS 614 (e.g. comparison of asignal quality to a threshold or relative to signal qualitiescorresponding to a beam included in the set of beam indexes 630).

In one aspect, the base station 602 and/or the UE 604 may maintain theset of beam indexes 630 as a candidate set. The base station 602 and/orthe UE 604 may simultaneously maintain both an active set of beamindexes and a candidate set of beam indexes. For a candidate set of beamindexes, the beams corresponding to the beam indexes in the set of beamindexes 630 may be maintained for inclusion in an active set of beamindexes. Similar to the active set of beam indexes, the base station 602and/or the UE 604 may update the candidate set of beam indexesperiodically, for example, based on measurements of a BRS 612 or BRRS614 (e.g. comparison of a signal quality to a threshold or relative tosignal qualities corresponding to a beam included in the candidate setof beam indexes). However, the periodicity for updating the active setof beam indexes may be different than the periodicity for updating thecandidate set of beam indexes.

The base station 602 and/or the UE 604 may update the set of beamindexes 630, for example, by adding a beam index to or removing a beamindex from a set of beam indexes 630. Additionally, the base station 602and/or the UE 604 may move a beam index between the active set of beamindexes and the candidate set of beam indexes. The criteria for updatinga set of beam indexes 630 may be based on a signal quality measurement,such as a received power for a BRS 612 or BRRS 614. For example, asignal quality may be compared to a threshold or to another signalquality corresponding to a beam index currently included in a set ofbeam indexes.

In various aspects, the base station 602 may communicate 640 with the UE604 through the fifth beam 620 e, which may be a current active beam orcurrent serving beam. The communication 640 may be performed with afirst RAT, such as a mmW RAT, a 5G RAT (e.g., based on one or moretechnical standards promulgated by 3GPP), and the like. Thecommunication 640 may be uplink communication, downlink communication,or both uplink and downlink communication.

In various aspects, the base station 602 may determine that beamtracking is to be performed with the UE 604. Beam tracking may includeone or more operations for selecting or identifying a beam of the set ofbeams 620 a-h for the communication 640 between the base station 602 andthe UE 604 (e.g., uplink and/or downlink communication). For example,the base station 602 may determine that the communication 640 throughthe fifth beam 620 e is degraded (e.g., a radio link failure) and/orthat another beam may provide better quality than the fifth beam 620 e.Thus, the base station 602 may determine that a new serving beam of thebeams 620 a-h may be used to communicate 640 with the UE 604.

Based on the determination that beam tracking is to be performed, thebase station 602 may perform beam tracking with the UE 604. In variousaspects, beam tracking may include one or more operations associatedwith identifying or selecting a new active or new serving beam forcommunication between the base station 602 and the UE 604.

According to one aspect of beam tracking, the base station 602 maytransmit at least one of the BRSs 612 a-h. The UE 604 may receive one ormore of the BRSs 612 a-h, each of which may correspond to a respectivebeam of the beams 620 a-h. The UE 604 may select or identify at leastone beam index corresponding to one of the beams 620 a-h based on thereception of the one or more BRSs 612 a-h (e.g., the UE 604 may identifyone or more BRSs 612 a-h having a highest signal quality). The UE 604may transmit, to the base station 602, a first indication of one or morebeam indexes corresponding to one or more of the beams 620 a-h having abest (e.g., highest) signal quality measured for a respective receivedBRS of the BRSs 612 a-h (e.g., a beam index corresponding to the sixthbeam 620 f). Based on the first indication of the one or more beamindexes, the base station 602 may transmit one or more BRRSs 614 c-f.For example, the base station 602 may transmit the BRRSs 614 c-f throughthe respective beams 620 c-f that are close or proximate to the one ormore beams corresponding to the one or more beam indexes indicated bythe first indication. The UE 604 may receive one or more of the BRRSs614 c-f, each of which may correspond to a respective beam of the beams620 c-f. The UE 604 may select or identify at least one beam indexcorresponding to one of the beams 620 c-f based on the reception of theone or more BRRSs 614 c-f (e.g., the UE 604 may identify one or moreBRRSs 614 c-f having a highest signal quality). The UE 604 may transmit,to the base station 602, a second indication of one or more beam indexescorresponding to one or more of the beams 620 c-f having a best (e.g.,highest) signal quality measured for a respective received BRRS of theBRRSs 614 c-f (e.g., a beam index corresponding to the sixth beam 620f). The base station 602 and the UE 604 may communicate through a newactive beam, which may correspond to the beam index indicated by thesecond indication, such as the sixth beam 620 f.

According to one aspect of beam tracking, the UE 604 may transmit arequest for beam tracking 648 (e.g., a BAR). The request for beamtracking 648 may request the base station 602 to transmit the BRRSs 614c-f. Based on the request for beam tracking 648, the base station 602may transmit the one or more BRRSs 614 c-f. For example, the basestation 602 may transmit the BRRSs 614 c-f through the respective beams620 c-f that are close or proximate to the first active beam (e.g., thefifth beam 620 e). The UE 604 may receive the one or more of the BRRSs614 c-f, each of which may correspond to a respective beam of the beams620 c-f. The UE 604 may select or identify at least one beam indexcorresponding to one of the beams 620 c-f based on the reception of theone or more BRRSs 614 c-f (e.g., the UE 604 may identify one or moreBRRSs 614 c-f having a highest signal quality). The UE 604 may transmit,to the base station 602, an indication of one or more beam indexescorresponding to one or more of the beams 620 c-f having a best (e.g.,highest) signal quality measured for a respective received BRRS of theBRRSs 614 c-f (e.g., a beam index corresponding to the sixth beam 620f). The base station 602 and the UE 604 may communicate through a newactive beam, which may correspond to the beam index indicated by theindication, such as the sixth beam 620 f.

In one aspect, the base station 602 may determine that beam tracking isto be performed with the UE 604 based on the communication 640 with theUE 604. For example, the base station 602 may transmit, to the UE 604, amessage 642 indicating that beam tracking is to be performed (e.g.,based on the determination that beam tracking is to be performed). In anaspect, the base station 602 may send the message 642 on a PDCCH (e.g.,xPDCCH) or a PDSCH (e.g., xPDSCH). In an aspect, the base station 602may send the message 642 as DCI on the PDCCH. For example, one or morebits associated with a DCI may be reserved to indicate the message 642,and the base station 602 may use the one or more reserved bits of theDCI to indicate the message to perform beam tracking. The reserved bitsmay vary according to DCI formats.

In one aspect, the base station 602 may transmit the message through thefifth beam 620 e, which may be a current active beam or current servingbeam. In other words, the base station 602 may transmit the message 642to the UE 604 using a first RAT (e.g., a mmW RAT). In another aspect,the base station 602 may transmit the message 642 to the UE through asecond RAT 610, which may have a lower carrier frequency than the firstRAT (e.g., a sub-6 GHz or LTE RAT).

In an aspect, the UE 604 may acknowledge the message 642, such as bytransmitting an ACK message. The UE 604 may transmit an acknowledgmentmessage through the first RAT or the second RAT 610. The base station602 and the UE 604 may then perform beam tracking using the first RAT.In aspect, the base station 602 may perform beam tracking (such as betransmitting the BRSs 612 a-h) when an acknowledgement is not receivedin response to the message 642 (e.g., within a predetermined period oftime).

In an aspect, the base station 602 may communicate with the UE 604 usingthe current active beam (e.g., fifth beam 620 e) by sending a referencesignal 644 to the UE 604. For example, the base station 602 may send thereference signal 644 to determine if the current active beam (e.g.,fifth beam 620 e) is failing. According to various aspects, thereference signal 644 may be a CSI-RS, a CRS, an SSS, an MRS, a DMRS, ora BRS (e.g., the BRS 612 e).

In an aspect, if the base station 602 does not receive a response to thereference signal 644, then the base station 602 may determine that thecurrent active beam (e.g., fifth beam 620 e) is failing. In anotheraspect, the UE 604 may transmit a response 646, for example, based onthe reference signal 644. The base station 602 may detect a radio linkfailure (e.g., determine that the current active beam is failing) basedon the response 646. For example, the base station 602 may detect aradio link failure by determining a value based on the response 646 andcomparing the value to a predetermined threshold.

In an aspect, the UE 604 may send the response 646 through the secondRAT 610 (e.g., a sub-6 GHz or LTE RAT). For example, the UE 604 maymeasure a value (e.g., a SINR, SNR, RSSI, RSRP, RSRQ, etc.) anddetermine that the current active beam is failing, and therefore, sendthe response 646 using the second RAT 610 in order to increase theprobability that the base station 602 receives the response 646. Inanother aspect, the UE 604 may send the response 646 through the firstRAT (e.g., the mmW RAT). The response 646 may include at least one of aCQI, an SINR, an SNR, an RSSI, an RSRP, an RSRQ, and the like.

In an aspect, the base station 602 may select and transmit referencesignals used for radio link failure for specific transmission points sothat reference signals are restricted to specific transmission points. Atransmission point may be, for example, different sectors of a same basestation and/or coordinated multipoint transmission from different basestations, such as where a controller indicates transmission propertiesto a base station. A transmission point may also be an antenna port ofone base station. For example, the base station 602 may select referencesignals (similar to the reference signal 644) to be transmitted in onesector that includes the UE 604. The base station 602 may allow separateradio link failure procedures for separate transmission ports.

The UE 604 may receive at least the first reference signal 644 and maymonitor this first reference signal 644 to determine whether there is anevent, which may be a Qin event or a Qout event. For a Qin event, the UE604 may measure one or more metrics (e.g., signal quality, receivedpower, RSSI, SNR, etc.) associated with the first reference signal 644to determine whether the one or more metrics are greater than or equalto a threshold. For a Qout event, the UE 604 may measure one or moremetrics (e.g., signal quality, received power, RSSI, SNR, etc.)associated with the first reference signal 644 to determine whether theone or more metrics are less than or equal to a threshold, which mayindicate radio link failure. In an aspect, the one or more metrics mayinclude at least an SNR or SINR.

In an aspect, the UE 604 may use the first reference signal 644 todetect radio link failure. In another aspect, the UE 604 may use aplurality of reference signals (including the reference signal 644) todetect radio link failure. For example, the UE 604 may use a best SNRestimate or another metric among all reference signals (including thereference signal 644) associated with a plurality of beams (e.g., thefourth beam 620 d, the fifth beam 620 e, the sixth beam 620 f). Inanother example, the UE 604 may combine one or more metrics measuredfrom the reference signals (including the reference signal 644) todetect radio link failure.

In an aspect, the UE 604 may maintain separate radio link failureprocesses for different receiving beams or subarrays, for example, usingthe reference signals associated with different receiving beams orsubarrays. For example, the UE 604 may maintain one process for thecurrent active beam (e.g., the fifth beam 620 e), which may be based onmonitoring the first reference signal 644. Further, the UE 604 maymaintain another process for a first candidate beam (e.g., the sixthbeam 620 f), which may be based on monitoring a second reference signal(e.g., the sixth BRS 612 f) associated with the first candidate beam(e.g., the sixth beam 620 f).

In an aspect, when the UE 604 detects a radio link failure, the UE 604and the base station 602 may perform beam tracking. In an aspect, the UE604 may request a beam tracking procedure with the base station 602 whena radio link failure is detected. For example, the UE 604 may transmit aBAR. In an aspect, the UE 604 may transmit an indication of the detectedradio link failure, for example, so that the base station 602 maydetermine to perform beam tracking with the UE 604.

In an aspect, base station 602 may determine that beam tracking is to beperformed with the UE 604 based on an absence of the communication 640.For example, the base station 602 may determine that beam tracking is tobe performed with the UE 604 when base station 602 expects the UE 604 totransmit one or more messages to the base station 602, but the one ormore messages are absent (e.g., for a predetermined period of time). Forexample, the base station 602 may schedule communication 640 with the UE604 on a PUCCH and/or a PUSCH. If the base station 602 determines thatthe communication 640 is absent on the PUCCH and/or PUSCH (e.g., whenthe UE 604 is scheduled), then the base station 602 may determine thatbeam tracking is to be performed with the UE 604. Similarly, if the basestation 602 is expecting an ACK/NACK message (e.g., to the message 642,to the reference signal 644, and the like), but the ACK/NACK message isabsent (e.g., for a predetermined period of time), then the base station602 may determine that beam tracking is to be performed with the UE 604.Similarly, if the base station 602 receives a plurality of NACK messages(e.g., a threshold amount of NACK messages before receiving an ACKmessage), then the base station 602 may determine that beam tracking isto be performed with the UE 604.

In an aspect, the UE 604 may operate according to DRX and, therefore,may alternate between continuous reception cycles (e.g., during whichthe UE 604 is active and receiving) and DRX cycles (e.g., during whichthe UE 604 is inactive and not receiving). The DRX may affect thecurrent active beam (e.g., the fifth beam 620 e), such as when the UE604 moves during DRX. Therefore, when the UE 604 transitions from DRX tocontinuous reception cycle, the UE 604 may use a synchronizationsubframe or a tracking subframe to find a beam. In an aspect, the basestation 602 may transmit a signal (e.g., a BRS 612 in a synchronizationsubframe or a BRRS 614 in a tracking subframe). In an aspect, thetracking signal may serve many UEs sharing a same DRX cycle. The UE 604may monitor a subset of tracking signals in a synchronization subframebased on one or more active beam indexes from a previous DRX cycle. Inanother aspect, the base station 602 may use the active beam of theprevious continuous reception cycle of the UE 604 to determine the beamindexes that the base station 602 should transmit during the beamtracking session.

In an aspect, the base station 602 may consider semi-persistentscheduling as a type of triggering for beam tracking, which may be basedon DRX durations (e.g., one PDCCH triggers multiple tracking signaltransmissions over multiple subframes). That is, the base station 602may determine that beam tracking is to be performed based on DRXdurations. In an aspect, the base station 602 may determine that beamtracking is to be performed with the UE 604 by determining a time atwhich the UE 604 is to transition from an inactive cycle of DRX to anactive cycle of DRX. For example, the current active beam (e.g., fifthbeam 620 e) may fail while the UE 604 is in an inactive DRX cycle. Thebase station 602 may be aware of DRX cycles for the UE 604 and maydetermine to perform beam tracking that corresponds to a time at whichthe UE 604 is to transition out of the inactive cycle and into an activecycle for reception.

In an aspect, the base station 602 may perform beam tracking based onthe first active beam. For example, the UE 604 may transition into aninactive DRX cycle when the current active beam (e.g., fifth beam 620 e)is being used. The UE 604 may not drift too far during the inactive DRXcycle, and so the base station 602 may use beams that are close to thecurrent active beam (e.g., fifth beam 620 e) when performing beamtracking after the UE 604 is in the inactive DRX cycle. The base station602 may transmit the message 642 indicating that beam tracking is to beperformed, for example, based on a time at which the UE 604 is totransition to an active DRX cycle from an inactive DRX cycle.

Referring to FIG. 7, a diagram of a wireless communications system 700is illustrated. The base station 702 may be an aspect of the basestation 602, the base station 502, the base station 310, the basestation 102, the mmW base station 180, and/or another base station. TheUE 704 may be an aspect of the UE 604, the UE 504, the UE 350, the UE104, the UE 182, and/or another UE.

In various aspects, the base station 702 and the UE 704 may communicatethrough a first active beam, such as the fifth beam 720 e. In aspects,the UE 704 may need to indicate a beam of the beams 720 a-h to the basestation 702, e.g., when the communication through the fifth beam 720 edeteriorates, when the UE 704 transitions from an inactive DRX cycle toan active DRX cycle, etc. However, the base station 702 may detecttransmission from the UE 704 in the direction of the fifth beam 720 e.

According to various aspects, the UE 704 may send, to the base station702, a request 750 to change the active beam. The request 750 mayindicate a beam index corresponding to a new beam. In an aspect, the UE704 may use a Zadoff-Chu sequence to indicate the beam change request.

In aspects, the UE 704 and the base station 702 may communicate throughthe fifth beam 720 e, which may be a current active beam. The UE 704 mayidentify or select a new beam, such as the sixth beam 720 f, forcommunication with the base station 702. For example, the UE 704 maydetermine that communication through the fifth beam 720 e isdeteriorating or unsatisfactory. The UE 704 may select or identify thesixth beam 720 f as the new beam, for example, based on measuring asignal quality of a BRS and/or BRRS transmitted through the sixth beam720 f. The UE 704 may generate a request 750 to change the active beamfrom the fifth beam 720 e to the sixth beam 720 f. The UE 704 maygenerate the request 750 to indicate a beam index corresponding to thesixth beam 720 f. The UE 704 may send the request 750 to the basestation 702.

In one aspect, the UE 704 may generate the request 750 to indicate thebeam index corresponding to the new beam (e.g., the sixth beam 720 f)based on a cyclic shift. For example, the UE 704 and/or the base station702 may maintain a mapping of one or more cyclic shifts to one or morerespective beam indexes. In a further example, one or more bits of therequest 750 may correspond to a beam index of the new beam. The UE 704may identify a cyclic shift corresponding to the sixth beam 720 f andmay send the request 750 with the identified cyclic shift correspondingto the sixth beam 720 f. Accordingly, the base station 702 may receivethe request 750 with the cyclic shift and identify the beam indexassociated with the cyclic shift in order to determine the sixth beam720 f corresponding to the beam index.

In one aspect, the UE 704 may generate the request 750 to indicate thebeam index corresponding to the new beam (e.g., the sixth beam 720 f)based on a spreading across symbols. For example, the UE 704 and/or thebase station 702 may maintain a mapping of one or more spreading acrosssymbols to one or more respective beam indexes. The UE 704 may identifya spread across symbols corresponding to the sixth beam 720 f and maysend the request 750 with the identified spread across symbolscorresponding to the sixth beam 720 f. Accordingly, the base station 702may receive the request 750 with the spread across symbols and identifythe beam index associated with the spread across symbols in order todetermine the sixth beam 720 f corresponding to the beam index.

In one aspect, the UE 704 may generate the request 750 to indicate thebeam index corresponding to the new beam (e.g., the sixth beam 720 f)based on one or more subcarriers that carries the request 750. Forexample, the UE 704 and/or the base station 702 may maintain a mappingof one or more subcarriers to one or more respective beam indexes. TheUE 704 may identify one or more subcarriers corresponding to the sixthbeam 720 f and may send the request 750 on the identified one or moresubcarriers corresponding to the sixth beam 720 f Accordingly, the basestation 702 may receive the request 750 one the one or more subcarriersand identify the beam index associated with the one or more subcarriersin order to determine the sixth beam 720 f corresponding to the beamindex.

Based on the beam index indicated by the request 750, the base station702 may change the active beam from the fifth beam 720 e to the sixthbeam 720 f. The base station 702 and the UE 704 may then communicatethrough the sixth beam 720 f The communication may be uplink and/ordownlink communication.

In an aspect, the UE 704 may use a subframe 740 in order to indicate thenew beam (e.g., because beamforming may not be required for RACH in acell provided by the base station 702). In aspects, the subframe 740 maybe a RACH subframe. The subframe 740 may include a plurality ofresources—e.g., 10 time resources (e.g., slots) and 12 frequencyresources (e.g., carriers). The subframe 740 may include resources 742for scheduling request (SR) (e.g., SR collection or region) andresources 744 for RACH (e.g., RACH collection or region). Each resourcemay include six physical resource blocks (PRBs), and each PRB mayinclude twelve tones.

In one aspect, at least one of the base station 702 and/or the UE 704may maintain a mapping between beams (e.g., beams 720 a-h) associatedwith a synchronization (e.g., BRS) session and/or RACH session. That is,the UE 704 may be configured to indicate a beam index using one or moreresources of a subframe 740, such as by transmitting a request 750 on atleast one resource corresponding to the beam index selected by the UE704.

In one aspect, the subframe 740 may include SR resources 742 (e.g., anSR collection). The UE 704 may indicate a selected beam on resourcesthat are not included in the SR resources 742. The UE 704 may beconfigured to select a beam of the beams 720 a-h, and each beam of thebeams 720 a-h may correspond to a beam index. The UE 704 may select abeam of the beams 720 a-h, for example, based on measuring a signalquality of one or more BRSs or BRRSs received through one or more of thebeams 720 a-h. For example, the UE 704 may select a new beam (e.g., thesecond beam 720 b), and the UE 704 may be configured to transmit therequest 750 as a RACH sequence in symbols 0 and/or 1 of the resourcesnot included in the SR resources 742 if the selected beam indexcorresponding to the new beam (e.g., the second beam 720 b) correspondsto one of beams 720 a-d. Similarly, the UE 704 may be configured totransmit the request 750 as a RACH sequence in a symbols 2 and/or 3 ofthe resources not included in the SR resources 742 if the selected beamindex corresponds to one of beams 720 e-h.

In one aspect, the UE 704 may indicate a specific beam within the rangeusing at least one subcarrier. For example, the UE 704 may indicate abeam within the range of beams 720 a-d by using at least one of a pairof subcarriers 770, 772, 774, 776. Similarly, the UE 704 may indicate abeam within the range of beams 720 e-h by using at least one of a pairof subcarriers 770, 772, 774, 776. For example, subcarriers 770 mayindicate a first beam of a range and, therefore, when the UE 704transmits a RACH sequence on symbols 0 and 1 and subcarriers 770(corresponding to a first beam within a range of beams), the UE 704 isindicating a selected first beam 720 a. By way of another example, theUE 704 may indicate a selected seventh beam 720 g by transmitting a RACHsequence on subcarriers 774 (corresponding to a third beam within arange of the beams) on symbols 2 and 3 (corresponding to the range ofbeams 720 e-h). By way of another example, the UE 704 may indicate aselected sixth beam 720 f by transmitting a RACH sequence on subcarriers772 (corresponding to a second beam within a range of beams) on symbols2 and 3 (corresponding to the range of beams 720 e-h). The base station702 may therefore determine a selected beam index based on the at leastthe resources on which the RACH sequence is transmitted, which areresources not included in the SR resources 742.

In another aspect, the UE 704 may use resources not included in the RACHresources 744 to indicate a selected beam. In an aspect, a BAR proceduremay be configured in the UE 704. For example, if a dedicated SR for BRRSrequest is configured to the UE 704, a PHY layer of the UE 704 maysignal a dedicated SR for BRRS request in the resources not included inthe RACH resources 744.

In an aspect, the UE 704 may only transmit on the resources not includedin the RACH resources 744 (including SR resources 742) when the UE 704is timing aligned with the base station 702. The number of availablecyclic shifts associated with the resources not included in the RACHresources 744 may be higher than those available in the RACH resources744. Accordingly, there may be a higher degree of freedom associatedwith the resources not included in the RACH resources 744 (e.g., 192degrees of freedom) compared to the RACH resources 744 (e.g., 48 degreesof freedom). For example, a plurality of UEs may be able to transmitrequests (e.g., requests for beam tracking and/or BRRS, a BAR, etc.) onthe resources not included in the RACH resources 744. That is, differentcyclic shifts and/or different spreading across symbols may be used todistinguish between different UEs at the base station 702. For example,the UE 704 may transmit a Zadoff-Chu sequence in two symbols, whereasanother UE may multiply a sequence with [+1, −1] and transmit thatproduct.

In an aspect, the UE 704 may select a transmission time for SR based onsymbol index of the strongest beam (e.g., a beam in which a strongestBRS is received during a synchronization subframe). In an aspect, the UE704 may transmit an SR during a subframe 740 if instructed by a higherlayer. For example, a PHY layer of the UE 704 may be provided with aplurality of parameters, including a band number N_(SR), cyclic shift v,a root u, a parameter f′, a system frame number (SFN), a BRStransmission period N_(BRS), a number of symbols N_(RACH) during thesubframe 740 for which the base station 702 may apply different beams(e.g., different receive beams), a number of subframes M (e.g., numberof RACH subframe) in each frame, an index of the current subframe m(e.g., current RACH subframe), a symbol with the strongestsynchronization beam S_(Sync) ^(BestBeam). The root u may be cellspecific. The UE 704 may calculate a symbol index 1 based on the SFN,N_(BRS), N_(RACcH), M, m, and S_(Sync) ^(BestBeam). For example,l=((S _(Sync) ^(BestBeam)−(SFN·M·N _(RACH) +m·N _(RACH))%N _(BRS)%N_(BRS))·N _(rep),

Where N_(rep) may denote the number of symbols dedicated to a singleRACH transmission (e.g., N_(rep)=2).

In one aspect, at least one of the base station 702 and/or the UE 704maintains a mapping between beams (e.g., beams 720 a-h associated with asynchronization (or BRS) session and the resources not included in theRACH resources 744. That is, the UE 704 may be configured to indicate abeam index using one or more resources of a subframe 740, such as bytransmitting a request 750 on at least one resource corresponding to thebeam index selected by the UE 704.

For example, the UE 704 may be configured to transmit the request 750 ina symbol 0 and 1 of the subframe 740 if the selected beam index (e.g.,the second beam 720 b) corresponds to one of beams 720 a-d. Similarly,the UE 704 may be configured to transmit the request 750 in a symbol 2and 3 of the subframe 740 if the selected beam index corresponds to oneof beams 720 e-h.

In one aspect, UE 704 may indicate a specific beam within the rangeusing at least one subcarrier. For example, the UE 704 may indicate abeam within the range of beams 720 a-d by using at least one of a pairof subcarriers 760, 762, 764, 766. Similarly, the UE 704 may indicate abeam within the range of beams 720 e-h by using at least one of a pairof subcarriers 760, 762, 764, 766. For example, subcarriers 760 mayindicate a first beam of a range and, therefore, when the UE 704transmits a request 750 on symbols 0 and 1 and subcarriers 760, the UE704 is indicating a selected first beam 720 a. By way of anotherexample, the UE 704 may indicate a selected seventh beam 720 g bytransmitting a request on subcarriers 764 (corresponding to a third beamwithin a range) on symbols 2 and 3 (corresponding to the range of beams720 e-h). The base station 702 may therefore determine a selected beamindex based on the at least one resource on which the request istransmitted.

Referring to FIG. 8, a diagram of a wireless communications system 800is illustrated. The base station 802 may be an aspect of the basestation 702, the base station 602, the base station 502, the basestation 310, the base station 102, the mmW base station 180, and/oranother base station. The UE 804 may be an aspect of the UE 704, the UE604, the UE 504, the UE 350, the UE 104, the UE 182, and/or another UE.

In FIG. 8, the UE 804 may communicate with the base station 802 using anactive beam 820 e (e.g., the active beam 820 e may be an aspect of oneof the beams 720 a-h described in FIG. 7, such as the fifth beam 720 e).The UE 804 may communicate with the base station 802 through a set ofbeams 840 d-e at the UE 804. In an aspect, the active beam 802 e may bepaired with a first beam 840 d at the UE 804, which may form an activebeam pair. Similarly, the control-information beam 820 f may be pairedwith a second beam at the UE 804, which may form a control-informationbeam pair. The UE 804 may identify beam pairs for communication (e.g.,uplink and/or downlink communication) with the base station 802. In oneaspect, the UE 804 may be configured to monitor a control channel (e.g.,a PDCCH, an ePDCCH, a new radio (NR) PDCCH, etc.) on one or more beampair links simultaneously and/or the UE 804 may monitor the controlchannel on different beam pair link(s) in different OFDM symbols.

The UE 804 and/or the base station 802 may each maintain a set ofcandidate beam indexes 830. In an aspect, the set of candidate beamindexes 830 includes at least a beam index corresponding to acontrol-information beam 820 f (e.g., the control-information beam 820 fmay be an aspect of one of the beams 720 a-h described in FIG. 7, suchas the sixth beam 720 f). The set of candidate beam indexes 830 mayinclude additional beams 720 d, 720 g, 720 h (e.g., as described withrespect to FIG. 7). The base station 802 and/or the UE 804 may maintainto the set of candidate beam indexes 830 to include additional beams 720d, 720 g, 720 h that are not currently used for communication with theUE 804 (e.g., the base station 802 may generate one or more of theadditional beams 720 d, 720 g, 720 h based on a request 750 to changethe active beam). In an aspect, the set of candidate beam indexes 830may include a set of beam pairs, such as the beam pair 820 f, 840 e.

The UE 804 and/or the base station 802 may each maintain a set of activebeam indexes, which may be similar to the set of candidate beam indexes830. The set of active beam indexes may include one or more beam indexesto be used for communication between the base station 802 and the UE 804(including the active beam 820 e). The base station 802 and/or the UE804 may maintain to the set of active beam indexes to include additionalbeams (e.g., another of beams 720 a-h), which may be used for uplink ordownlink communication between the base station 802 and the UE 804. Inan aspect, the set of active beam indexes may include a set of beampairs, such as the beam pair 820 e, 840 d.

The base station 802 and the UE 804 may maintain two sets of beams: anactive set and a candidate set. The active set may include the activebeam 820 e. The candidate set may include at least one beam that may bea candidate for communication between the base station 802 and the UE804 (e.g., if the active beam 820 e fails). In one aspect, the candidatebeam set may include the control-information beam 820 f.

In one aspect, the UE 804 transmits control information on a controlchannel so that it is received at the base station 802 using the activebeam 820 e. In an aspect, the control channel may be a PUCCH. However,the base station 802 may periodically receive control information 844carried on the control channel through a second beam. For example, theUE 804 may send control information 844 to the base station 802 using acontrol-information beam 820 f. In an aspect, the control-informationbeam 820 f may correspond with a second beam 840 e at the UE 802.Therefore, the UE 804 may identify or select the second beam 840 ethrough which to send the control information 844 based on usage of thecontrol-information beam 820 f instead of the active beam 820 e.

In an aspect, the UE 804 and the base station 802 may be furtherconfigured to communicate using a wide beam 822. For example, the basestation 802 and the UE 804 may communicate using a mmW RAT or near-mmWRAT in which beamforming weights for the active beam 820 e andcontrol-information beam 820 f may have a first beam weight, whereas thewide beam 822 may have a second beam weight that is greater than thefirst beam weight. In an aspect, the base station 802 may sample antennaweights of the base station 802 such that a wider area of a sectorassociated with the base station 802 is covered. In an aspect, the widebeam 822 may have an angle that is greater than the angle of at leastone of the active beam 820 e and/or the control-information beam 820 fFor example, the active beam 820 e and/or the control-information beam820 f may have an angle of approximately five or six degrees, whereasthe wide beam 822 may have an angle of approximately twenty or thirtydegrees.

In one aspect, the wide beam 822 may be directed toward at least onebeam at the UE 804. For example, the wide beam 822 may be directedtoward the second beam 840 e at the UE 804 and, therefore, when the UE804 monitors the antenna port or subarray associated with the secondbeam 840 e, the UE 804 may receive information transmitted by the basestation 802 through the wide beam 822.

In an aspect, the UE 804 may periodically send information 844 (e.g.,control information) to the base station 802 through the wide beam 822.The UE 804 may measure a signal quality or channel estimate associatedwith communication with the base station 802. For example, the UE 804may measure a signal quality (e.g., SNR, SINR, received power, receivedquality, etc.) for a signal (e.g., a BRS, a CSI-RS, a reference signal,etc.), and the UE 804 and may send the signal quality or channelestimate to the base station 802. In various aspects, the informationmay include UCI, CQI, SR, and/or other control information. The basestation 802 may receive the signal quality or channel estimate throughthe wide beam 822, for example, if the active beam 820 e and/or thecontrol-information beam 820 f fail and/or become unsatisfactorilydegraded.

In an aspect, the UE 804 may send the information (e.g., controlinformation 844 on a control channel, such as a PUCCH) through the widebeam 822 without explicit signaling from the base station 802. Forexample, the UE 804 may determine that the UE 804 is to send informationthrough the wide beam 822 after an absence of signaling from the basestation 802 on the active beam 820 e and/or the control-information beam820 f.

Accordingly, the base station 802 may receive information (e.g., thecontrol information 844) from the UE 804 through the wide beam 822. Inan aspect, the base station 802 may determine that at least one of theactive beam 820 e and/or the control-information beam 820 f have failedand/or become unsatisfactorily degraded based on reception of theinformation through the wide beam 822.

In an aspect, the UE 804 may periodically send the control information844 on the control channel through the control-information beam 820 f.The base station 802 may estimate uplink channel quality for thecontrol-information beam 820 f based on the periodic reception of thecontrol information 844 from the UE 804. In one aspect, the UE 804 maymeasure a quality (e.g., channel quality) associated with the activebeam 820 e and may generate the control information 844 to include anindication of the quality associated with the active beam 820 e.

The base station 802 receive the information 844. Based on information844, the base station 802 may determine whether the active beam 820 e isfailing and/or is unsatisfactory (e.g., the quality does not satisfy athreshold).

While FIG. 8 illustrates the communication of the information 844through the control-information beam 820 f, the wide beam 822 may serveas the control-information beam, as described. For example, the UE 804may send the information 844 through a beam corresponding to a beamindex included in a set of candidate beams and/or the UE 804 may sendthe information 844 through the wide beam 822.

The UE 804 and the base station 802 may switch to a beam correspondingto a beam index included in a the set of candidate beam indexes forcommunication based on the control information 844. For example, the UE804 and the base station 802 may switch to the control-information beam820 f for communication (in which case the control-information beam 820f may become the active beam and may carry other data instead or inaddition to the control information 844).

In one aspect, the UE 804 and the base station 802 may change the activebeam to the control-information beam 820 f without explicit signaling(e.g., the UE 804 does not need to transmit through RACH or SR toindicate beam index, as described in FIG. 7). For example, the UE 804may determine that the active beam is to be changed based on theinformation 844 (e.g., based on a signal quality included in theinformation 844). Similarly, the base station 802 may determine that theactive beam is to be changed based on the information 844.

In an aspect, the base station 802 may transmit, to the UE 804,information 842 indicating the periodicity at which control informationis to transmitted on a control channel from the UE 804 to the basestation 802. In one aspect, the base station 802 may transmit theinformation 842 through the active beam 820 e. In one aspect, the basestation 802 may transmit the information 842 to the UE 804 using RRCsignaling. In another aspect, the base station 802 may transmit theinformation 842 to the UE 804 on a PDCCH. For example, the base station802 the information 842 may indicate the periodicity to the UE 804 usingone or more bits of DCI (e.g., one or more bits reserved for information842 indicating the periodicity) and/or via a DCI format.

The UE 804 may receive the information 842 and may determine theperiodicity based on the information 842. The UE 804 may periodicallytransmit the control information 844 to the base station 802 at thedetermined periodicity.

FIGS. 9A, 9B, 9C, 9D, 9E illustrate an example wireless communicationenvironment including at least a base station 902 and UE 904. The basestation 902 may be an aspect of the base station 802, the base station702, the base station 602, the base station 502, the base station 310,the base station 102, the mmW base station 180, and/or another basestation. The UE 904 may be an aspect of the UE 804, the UE 704, UE 604,the UE 504, the UE 350, the UE 104, the UE 182, and/or another UE.

The UE 904 may include one or more antenna arrays and/or one or moresubarrays. The UE 904 may receive, from the base station 902, one ormore reference signals (e.g., PSS/BRS, a discrete prolate spheroidalsequence (DPSS), a CSI-RS, a BRRS, etc.) through one or more beams,which may be received at multiple antennas of the UE 904 in accordancewith multiple receive angle ranges, which may be detected at the UE 904at receive combiner(s). Data communication between the base station 902and the UE 904 may require a combination of one or more of: a best beamat the base station 902 (corresponding to a beam index), a best subarrayat the UE 904 (e.g., a subarray at which a highest received power of oneor more reference signals is detected), and/or a best receive combinerat the best array or subarray at the UE 904 (e.g., a receive combiner atwhich a highest received power of one or more reference signals isdetected).

In an example, the base station 902 may sweep through the transmitdirections according to a sequence A-B-C-D in order to transmit one ormore reference signals (e.g., reference signals 950). In anotherexample, the base station 902 may sweep through the transmit directionsaccording to the sequence B-D-A-C. Although only four transmitdirections and two transmit sequences are described with respect to FIG.9A, any number of different transmit directions and transmit sequencesare contemplated.

In aspects, the base station 902 may send out a reference signal (e.g.,the reference signals 950) on a plurality of successive symbols,although in different directions A-B-C-D. The base station 902 may sweepthrough the entire sector.

Referring to diagram 920, the UE 904 may listen or detect for referencesignals in different receive directions (e.g., directions E, F, G, andH). In an example, the UE 904 may sweep through the receive directionsaccording to a sequence E-F-G-H. In another example, the UE 904 maysweep through the receive directions according to the sequence F-H-E-J.Although only four receive directions and two receive sequences aredescribed, any number of different receive directions and receivesequences are contemplated.

In aspects, the UE 904 may try out different receive subarrays atdifferent periods, such as four reference signal periods. The UE 904 mayfind the best subarray after the reference signal period(s). Forexample, the UE 904 may measure a signal quality for each referencesignal received at a respective subarray during a respective period.

The UE 904 may determine the best subarray as the subarray having ahighest signal quality measured for a reference signal, the subarrayhaving a highest average signal quality for the set of reference signalsreceived during the period in which that subarray is used, or anothermethod of selecting a best subarray.

FIG. 9C illustrates an aspect of a reference signal 950. The referencesignal 950 may be repeated in successive subframes, slots, or subslots.Fourteen symbols may be reserved for the reference signal 950; however,the reference signal 950 may not be transmitted during each symbol. Forexample, a reference signal 950 may be transmitted through a first beamon one symbol of the fourteen symbols, and another reference signal maybe transmitted through a second beam on a different symbol of thefourteen symbols. The reference signal may be one or more of a PSS, SSS,BRS, BRRS, CSI-RS, DPSS, and the like.

FIG. 9D illustrates a wireless communication system 960 in which a slot962 includes fourteen symbols. One or more of the fourteen symbols maybe used for a reference signal, such as the reference signal 950. In theillustrated aspect, the base station 902 may transmit three beams 970,972, 974 (e.g., a fine beam set). The base station 902 may transmit areference signal through the set of beams 970, 972, 974 in the lastthree symbols 964, 966, 968 of the slot 962.

The base station 902 may cause the reference signal to occupy one out ofevery fourth tone in each symbol of the three symbols 964, 966, 968. Thebase station 902 may repeat the reference signal four times in eachsymbol of the three symbols 964, 966, 968.

In aspects, the UE 904 may try out different receive combiners atdifferent periods, such as four reference signal periods for each of thethree symbols 964, 966, 968. The UE 904 may find the best receivecombiner after the reference signal period(s). For example, the UE 904may measure a signal quality for each reference signal received at arespective receive combiner during a respective period. The UE 904 maydetermine a best receive combiner by determining the receive combiner atwhich a highest signal quality is measured for a reference signal, thereceive combiner at which the highest average signal quality is measuredfor the set of reference signals received during the period in which thereceive combiner is used, or another method of selecting a best receivecombiner.

Additionally, the UE 904 may select a best beam corresponding to a beamindex at the base station 902 based on the reference signals receivedduring the three symbols 964, 966, 968. For example, the UE 904 maydetermine a highest signal quality corresponding to reference signalreceived during one of the three symbols 964, 966, 968. The UE 904 maydetermine a beam index corresponding to a beam at the base station 902,for example, because each set of symbols of the three symbols 964, 966,968 may correspond to a different beam. The UE 904 may communicate withthe base station 902 through the best beam corresponding to the beamindex (e.g., the UE 904 may send information indicating the beam indexto the base station 902).

FIG. 9E illustrates an example wireless communication environment 980including at least a base station 902 and UE 904. In aspects, the basestation 902 may need to convey one or more beam indexes to the UE 904,for example, to initiate reference signals transmission. In an aspect,the reference signal may include one or more of a BRRS, BRS, CSI-RS,PSS, SSS, DPSS, MRS, and the like. Based on the reference signaltransmissions, the UE 904 may determine a best subarray and/or receivecombiner at the UE 904.

The base station 902 may determine one or more indexes associated withone or more beams 972, 974, 974. According to one aspect, the basestation 902 may receive one or more beam indexes corresponding to theone or more beams 972, 974, 976, for example, as BSI. The base station902 may determine that one or more reference signals are to betransmitted through the one or more beams corresponding to the one ormore beam indexes most recently indicated to the base station 902 by theUE 904.

For example, during reference signal transmission, the base station 902may transmit different types of beams. In one aspect, the base station902 may transmit BRS beams (e.g., coarse beams). The base station 902may need to convey one or more indexes associated with one or more BRSbeams to the UE 904. In such an aspect, nine bits may be required if theBRS duration period is four slots or subframes—e.g., the number ofsymbols per subframe is fourteen with eight antenna ports. The UE 904may send, to the base station 902, information indicating one or morebeam indexes corresponding to the one or more beams 972, 974, 976through which one or more BRSs are received.

According to another aspect, the base station 902 may determine the oneor more indexes associated with one or more beams 972, 974, 974 based onpreviously reported beams from the UE 904. For example, the base station902 may transmit the most recent beams that the UE 904 may havereported. For example, the UE 904 may report one or more beam indexesbased on one or more BRSs received through one or more beams (e.g., thebeams 972, 974, 976), which may be transmitted by the base station 902during a synchronization slot or subframe.

In aspects, the UE 904 may transmit information indicating the beamindexes (e.g., BSI) to the base station 902 through PUCCH or PUSCH(e.g., the UE 904 may be able to transmit more information through thePUSCH than the PUCCH). The set of beams used to train the UE 904 receivebeams may be implicitly derived based on the latest reported informationand/or channel types used to convey that information.

In one aspect, if the base station 902 schedules the reference signal inone or two symbols, the base station 902 may reuse beam information thatthe base station received on the PUCCH from the UE 904. In anotheraspect, if the base station 902 schedules the reference signal in morethan two symbols, the base station 902 may reuse beam information thatthe base station 902 received during the PUSCH from the UE 904. The basestation 902 may utilize a few bits (e.g., less than nine) to send, tothe UE 904, information 990 indicating the one or more beam indexes ofthe one or more previously reported beams.

In another aspect, the base station 902 may determine the one or morebeam indexes based on finer beams 972, 974, 974 previously transmittedto the UE 904. The finer beams 972, 974, 974 may have been previouslyused for transmission of one or more reference signals (e.g., MRS,CSI-RSs, and/or BRRSs). The base station 902 may only need to transmit afew bits (e.g., less than nine) to send, to the UE 904, information 990indicating the fine beams 972, 974, 974.

Based on the determined one or more beams indexes, the base station 902may transmit information 990 indicating the one or more beams indexes tothe UE 904. The base station 902 may transmit the information 990 on acontrol channel. In an aspect, the control channel may include a PDCCH.For example, the information 990 may be included in one or more bits ofa DCI message of the PDCCH.

Based on the information 990, the UE 904 may determine the one or morebeam indexes used for reference signals indicated by the information990. Thereafter, the base station 902 may transmit one or more referencesignals to the UE 904 through the one or more beams 972, 974, 976corresponding to the one or more beam indexes.

The UE 904 may use the best subarray and/or receive combiner to detectthe reference signal transmission. For example, the UE 904 may determinethe best subarray and/or receive combiner for a symbol in which thereference signal is scheduled to be transmitted. The UE 904 may thendetect for the reference signal using the determined subarray and/orreceive combiner.

FIGS. 10A and 10B are flowcharts of method 1000, 1020 of wirelesscommunication. The methods 1000, 1020 may be performed by a base station(e.g., the base station 602). In one aspect, the methods 1000, 1020 maybe performed by an apparatus. One of ordinary skill would understandthat one or more operations may be omitted, transposed, and or performedcontemporaneously.

Beginning with FIG. 10A at operation 1002, the base station may transmitat least one BRS. For example, the base station may generate a set ofBRSs and the base station may transmit the set of BRSs through a set ofbeams to be used for communication with a UE. In the context of FIG. 6,the base station 602 may transmit the set of BRSs 612 a-h through theset of beams 620 a-h, and each BRS of the BRSs 612 a-h may correspond toa beam of the beams 620 a-h.

At operation 1004, the base station may receive, from the UE, anindication of a first beam index based on the BRS. The first beam indexmay be a coarse beam index to be used for beam refinement. In thecontext of FIG. 6, the base station 602 may receive, from the UE 604, anindication of a beam index corresponding a coarse beam, such as thesixth beam 620 f. The indication may be the first indication 560, asdescribed in FIG. 5.

At operation 1006, the base station may transmit, based on the firstindication of the first beam index, at least one BRRS. In the context ofFIG. 6, the first indication may indicate a beam index corresponding tothe sixth beam 620 f, and the base station may transmit a fine beam set,such as by transmitting the BRRS 614 c-f on beams 620 c-f that are closeto the beam indicated by the coarse beam index.

At operation 1008, the base station may receive, based on the at leastone BRRS, a second indication of a second beam index corresponding to asecond beam. In the context of FIG. 6, the base station 602 may receive,from the UE 604, an indication of a beam index corresponding a finebeam, such as the sixth beam 620 f. The indication may be the secondindication 565, as described in FIG. 5.

The base station may communicate with the UE through the beamcorresponding to the index indicated in the second indication. Thecommunication may be uplink communication and/or downlink communication.

Turning to FIG. 10B, another method 1020 is illustrated for a basestation performing beam tracking. At operation 1022, the base stationmay receive, from a UE, a request for beam tracking. For example, thebase station may receive a BAR. In the context of FIG. 6, the basestation 602 may receive, from the UE 604, a request for beam tracking.

At operation 1024, the base station may transmit, based on the requestfor beam tracking, at least one BRRS. In the context of FIG. 6, the basestation may transmit a fine beam set, such as by transmitting the BRRSs614 c-f on beams 620 c-f that are close to a beam through which the basestation 602 and the UE 604 previous communication (e.g., the fifth beam620 e).

At operation 1026, the base station may receive, based on the at leastone BRRS, a second indication of a second beam index corresponding to asecond beam. In the context of FIG. 6, the base station 602 may receive,from the UE 604, an indication of a beam index corresponding a finebeam, such as the sixth beam 620 f. The indication may be the secondindication 565, as described in FIG. 5.

The base station may communicate with the UE through the beamcorresponding to the index indicated in the second indication. Thecommunication may be uplink communication and/or downlink communication.

FIGS. 11A and 11B are flowcharts of method 1100, 1120 of wirelesscommunication. The methods 1100, 1120 may be performed by a UE (e.g.,the UE 604). In one aspect, the methods 1100, 1120 may be performed byan apparatus. One of ordinary skill would understand that one or moreoperations may be omitted, transposed, and or performedcontemporaneously.

Beginning with FIG. 11A at operation 1102, the UE may receive, from abase station, at least one BRS. In the context of FIG. 6, the UE 604 mayreceive, from the base station 602, the set of BRSs 612 a-h through theset of beams 620 a-h, and each BRS of the BRSs 612 a-h may correspond toa beam of the beams 620 a-h.

At operation 1104, the UE may transmit, to the base station, anindication of a first beam index based on the BRS. The first beam indexmay be a coarse beam index to be used for beam refinement. For example,the UE may measure a signal quality or power for one or more of thereceived BRSs and select a beam index corresponding to a beam throughwhich the BRS having a best or highest value is received. In the contextof FIG. 6, the UE 604 may transmit, to the base station 602, anindication of a beam index corresponding a coarse beam, such as thesixth beam 620 f The indication may be the first indication 560, asdescribed in FIG. 5.

At operation 1106, the UE may receive, from the base station (e.g.,based on the first indication of the first beam index), at least oneBRRS. In the context of FIG. 6, the UE 604 may receive a fine beam set,such as by receiving the BRRSs 614 c-f on beams 620 c-f that are closeto the beam indicated by the coarse beam index.

At operation 1108, the UE may transmit, based on the at least one BRRS,a second indication of a second beam index corresponding to a secondbeam. The second beam index may be a fine beam index to be used forcommunication. For example, the UE may measure a signal quality or powerfor one or more of the received BRRSs and select a beam indexcorresponding to a beam through which the BRRS having a best or highestvalue is received. In the context of FIG. 6, the UE 604 may transmit, tothe base station 602, an indication of a beam index corresponding a finebeam, such as the sixth beam 620 f. The indication may be the secondindication 565, as described in FIG. 5.

The UE may communicate with the UE through the beam corresponding to theindex indicated in the second indication. The communication may beuplink communication and/or downlink communication.

Turning to FIG. 11B, another method 1120 is illustrated for a basestation performing beam tracking. At operation 1122, the UE maytransmit, to the base station, a request for beam tracking. For example,the UE may transmit a BAR. In the context of FIG. 6, the UE 604 maytransmit, to the base station 602, a request for beam tracking 648(e.g., a BAR).

At operation 1124, the UE may receive, from the base station based onthe request for beam tracking, at least one BRRS. In the context of FIG.6, the UE 604 may receive a fine beam set, such as by receiving the BRRS614 c-f on beams 620 c-f that are close to a beam through which the basestation 602 and the UE 604 previous communication (e.g., the fifth beam620 e).

At operation 1126, the UE may transmit, to the base station and based onthe at least one BRRS, an indication of a beam index corresponding to abeam. For example, the UE may measure a signal quality or power for oneor more of the received BRRSs and select a beam index corresponding to abeam through which the BRRS having a best or highest value is received.In the context of FIG. 6, the UE 604 may transmit, to the base station602, an indication of a beam index corresponding a fine beam, such asthe sixth beam 620 f. The indication may be the second indication 565,as described in FIG. 5.

The base station may communicate with the UE through the beamcorresponding to the index indicated in the indication. Thecommunication may be uplink communication and/or downlink communication.

FIG. 12 is a flowchart of method 1200 of wireless communication. Themethod 1200 may be performed by a base station (e.g., the base station602). In one aspect, the method 1200 may be performed by an apparatus.One of ordinary skill would understand that one or more operations maybe omitted, transposed, and or performed contemporaneously.

Beginning with operation 1202, the base station may communicate with aUE through a first active beam. In an aspect, the communication may bedownlink communication. For example, the base station may determine datato be transmitted to the UE and then the base station may send thedetermined data through the first active beam. In an aspect, thecommunication may be uplink communication. For example, the base stationmay determine a time (e.g., slot) at which the UE is scheduled to senddata to the base station, and then the base station may receive the datathrough the first active beam at the scheduled time. In the context ofFIG. 6, the base station 602 may communicate with the UE 604 through afirst active beam, such as the fifth beam 620 e.

In an aspect, operation 1202 may include operation 1220. At operation1220, the base station may send, to the UE, a reference signal todetermine if the first active beam is failing. In an aspect, thereference signal may be a CSI-RS, a CRS, an SSS, an MRS, a DMRS, or aBRS. In the context of FIG. 6, the base station 602 may send thereference signal 644 through the first active beam (e.g., the fifth beam620 e).

At operation 1204, the base station may determine that beam tracking isto be performed with the UE. For example, the base station may determinethat the first active beam is failing, and then the base station mayinitiate beam tracking in order to select a new active beam. In thecontext of FIG. 6, the base station 602 may determine that beam trackingis to be performed with the UE 604.

In an aspect, operation 1204 may include operation 1222 and operation1224. At operation 1222, the base station may receive a response fromthe UE based on a reference signal transmitted to the UE (e.g., thereference signal described at operation 1220). In an aspect, theresponse may include at least one of a CQI, an SINR, an SNR, an RSSI, anRSRP, or an RSRQ. In the context of FIG. 6, the base station 602 mayreceive, from the UE 604, the response 646.

At operation 1224, the base station may detect a radio link failurebased on the received response. For example, the base station maydetermine that a value (e.g., a CQI, SINR, SNR, RSRP, RSRQ, etc.) may bebelow a threshold, and the base station may determine that the valuebeing below the threshold indicates a radio link failure. In anotherexample, the base station may determine that the response indicates aNACK or that the response is absent, and the base station may determinea radio link failure has occurred based on the NACK or the absence ofthe response. In the context of FIG. 6, the base station 602 may detectthe radio link failure through the first active beam (e.g., the fifthbeam 620 e) based on the response 646 or based on the absence of theresponse 646.

In another aspect, operation 1204 may include operation 1226. Atoperation 1226, the base station may determine a time at which the UE isto transition from an inactive cycle of DRX to an active cycle of DRX.Because the base station and the UE may not communicate while the UE isin an inactive DRX cycle, the base station may determine that beamtracking is to be performed with the UE when the UE transition to anactive cycle of DRX (e.g., because the UE may have shifted during theinactive DRX cycle). In the context of FIG. 6, the base station 602 maydetermine DRX cycles for the UE 604 (e.g., the base station 602 mayconfigure DRX cycles for the UE 604), and when the UE 604 is totransition from an inactive DRX cycle to an active DRX cycle, the basestation 602 may determine that the beam tracking is to be performed withthe UE 604.

In another aspect, operation 1204 may include operation 1228. Atoperation 1228, the base station may determine an absence ofcommunication with the UE using the first active beam. For example, thebase station may determine that the base station is not receiving datafrom the UE when the UE is scheduled to communicate with the basestation. In another example, the base station may receive one or moreNACK messages that indicate an absence of communication with the UE. Inthe context of FIG. 6, the base station 602 may determine an absence ofthe communication 640 with the UE 604 using the first active beam (e.g.,the fifth beam 620 e).

At operation 1206, the base station may perform beam tracking with theUE based on the determination that the beam tracking is to be performed.For example, the base station may perform one or more operationsdescribed with respect to FIG. 10A and/or 10B. In the context of FIG. 6,the base station 602 may perform beam tracking with the UE 604.

In an aspect, operation 1206 includes operation 1230. At operation 1230,the base station may send, to the UE, a message indicating that beamtracking is to be performed. The base station may send the message on aPDCCH or a PDSCH. In the context of FIG. 6, the base station 602 maysend, to the UE 604, the message 642 indicating that beam tracking is tobe performed. The base station 602 may then perform one or moreoperations described with respect to FIGS. 10A and/or 10B.

At operation 1208, the base station may communicate with the UE throughthe second active beam based on the beam tracking. For example, the basestation may receive, from the UE, an indication of a beam indexcorresponding to a beam at the base station. The base station may selectthe beam corresponding to the indicated beam index for at least one ofuplink or downlink communication with the UE. In the context of FIG. 6,the base station 602 may communicate with the UE 604 through the secondactive beam (e.g., the sixth beam 620 f).

FIG. 13 is a flowchart of method 1300 of wireless communication. Themethod 1300 may be performed by a UE (e.g., the UE 604). In one aspect,the method 1300 may be performed by an apparatus. One of ordinary skillwould understand that one or more operations may be omitted, transposed,and or performed contemporaneously.

Beginning with operation 1302, the UE may communicate with a basestation through a first active beam. In an aspect, the communication maybe downlink communication. For example, the UE may receive data to fromthe base station. In an aspect, the communication may be uplinkcommunication. For example, the UE may determine a time (e.g., slot) atwhich the UE is scheduled to send data to the base station, and then theUE may transmit the data through the first active beam at the scheduledtime. In the context of FIG. 6, the UE 604 may communicate with the basestation 602 through a first active beam, such as the fifth beam 620 e.

In an aspect, operation 1302 may include operation 1320. At operation1320, the UE may receive, from the base station, a reference signal. Inan aspect, the reference signal may be a CSI-RS, a CRS, an SSS, an MRS,a DMRS, or a BRS. In the context of FIG. 6, the UE 604 may receive, fromthe base station 602, the reference signal 644 through the first activebeam (e.g., the fifth beam 620 e).

At operation 1304, the UE may receive, from the base station, a signalassociated with beam tracking. In an aspect, the signal may be thereference signal. In another aspect, the signal may be a BRS. In anotheraspect, the signal may be a BRRS. In another aspect, the signal may be amessage indicating that beam tracking is to be performed between the UEand the base station. In the context of FIG. 6, the UE 604 may receive,from the base station 602, a signal associated with beam tracking. Thesignal may be a BRS of the BRSs 612 a-h, a BRRS of the BRRSs 614 c-f,the message 642, the reference signal 644, or another signal.

In an aspect, operation 1304 may include operation 1322 and operation1324. At operation 1322, the UE may detect a radio link failure based onreception of the reference signal (as described at operation 1320). Forexample, the UE may measure a signal quality (e.g., an SINR, an SNR, aBRSRP, an RSRP, an RSRQ, or another signal quality) and compare themeasured signal quality to a threshold. Based on the comparison, the UEmay determine that communicate through the first active beam is failingor degraded. In the context of FIG. 6, the UE 604 may detect a radiolink failure associated with the first active beam (e.g., the fifth beam620 e) based on reception of the reference signal 644.

At operation 1324, the UE may send an indication of the detected radiolink failure to the base station based on the detected radio linkfailure. For example, the UE may send a measured signal qualityassociated with the reference signal (e.g., an SINR, an SNR, a BRSRP, anRSRP, an RSRQ, etc.), a CQI, or a BAR, or another indication of thedetected radio link failure to the base station. In the context of FIG.6, the UE 604 may send the response 646 to the base station 602.

In an aspect, operation 1304 may include operation 1326. At operation1326, the UE may send, to the base station, a beam index based on a BRS.For example, the UE may measure signal qualities for a plurality of BRSsand may determine a best (e.g., highest) signal quality corresponding toa best BRS. The UE may determine a beam index corresponding to the beamthrough which the best BRS is received and may send the determined beamindex to the base station. In an aspect, this beam index may be a coarsebeam index. In the context of FIG. 6, the UE 604 may send, to the basestation 602, a beam index corresponding to a beam of the beams 620 a-hthrough which a best BRS of the BRSs 612 a-h is received. For example,the UE 604 may send the first indication 560, as described in FIG. 5.

In an aspect, operation 1304 may include operation 1328. At operation1328, the UE may send, to the base station, a beam index based on aBRRS. For example, the UE may measure signal qualities for a pluralityof BRRSs and may determine a best (e.g., highest) signal qualitycorresponding to a best BRRS. The UE may determine a beam indexcorresponding to the beam through which the best BRRS is received andmay send the determined beam index to the base station. In an aspect,this beam index may be a fine beam index. In the context of FIG. 6, theUE 604 may send, to the base station 602, a beam index corresponding toa beam of the beams 620 c-f through which a best BRRS of the BRRSs 614c-f is received. For example, the UE 604 may send the second indication565, as described in FIG. 5.

At operation 1306, the UE may perform beam tracking with the basestation, for example, based on the signal associated with beam tracking.For example, the UE may perform one or more operations described withrespect to FIG. 11A and/or 11B. For example, the UE 604 may send therequest for beam tracking 648. Based on the beam tracking, the UE maydetermine a second beam corresponding to a second beam index forcommunication with the base station. In the context of FIG. 6, the UE604 may perform beam tracking with the base station 602.

At operation 1308, the UE may communicate with the base station throughthe second active beam based on the beam tracking. For example, the UEmay transmit, to the base station, an indication of a beam indexcorresponding to a beam at the base station. The UE may select secondactive beam for at least one of uplink or downlink communication withthe UE. In the context of FIG. 6, the UE 604 may communicate with thebase station 602 through the second active beam (e.g., the sixth beam620 f).

FIG. 14 is a flowchart of method 1400 of wireless communication. Themethod 1400 may be performed by a base station (e.g., the base station702 and/or the base station 802). In one aspect, the method 1400 may beperformed by an apparatus. One of ordinary skill would understand thatone or more operations may be omitted, transposed, and or performedcontemporaneously.

Beginning with operation 1402, the base station may communicate with aUE through a first active beam. In an aspect, the communication may bedownlink communication. For example, the base station may determine datato be transmitted to the UE and then the base station may send thedetermined data through the first active beam. In an aspect, thecommunication may be uplink communication. For example, the base stationmay determine a time (e.g., slot) at which the UE is scheduled to senddata to the base station, and then the base station may receive the datathrough the first active beam at the scheduled time. In the context ofFIG. 7, the base station 702 may communicate with the UE 704 through afirst active beam, such as the fifth beam 720 e. In the context of FIG.8, the base station 802 may communicate with the UE 804 through theactive beam 820 e.

At operation 1404, the base station may transmit, to the UE, informationindicating a periodicity at which control information is to becommunicated on a control channel through a control-information beam.For example, the base station may determine a periodicity at whichcontrol information is to be sent to the base station by the UE (e.g.,based on one or more standards promulgated by 3GPP). The base stationmay generate a message that indicates the periodicity and may transmitthe generated message to the UE, for example, through the active beam.In the context of FIG. 7, the base station 702 may transmit, to the UE704, information indicating the periodicity through a current activebeam, such as the fifth beam 720 e. In the context of FIG. 8, the basestation 802 may transmit, to the UE 804, the information 842 indicatingthe periodicity through the active beam 820 e.

In one aspect, the base station may transmit the information indicatingthe periodicity to the UE through RRC signaling. In another aspect, thebase station may transmit the information indicating the periodicity tothe UE on a PDCCH. For example, the base station may indicate theinformation in DCI of the PDCCH, such as one or more bits of one or moreDCI formats that are reserved for information indicating theperiodicity.

At operation 1406, the base station may communicate, with the UE, thecontrol information on the control channel through thecontrol-information beam at the periodicity. For example, the basestation may receive (e.g., attempt to receive, detect for, monitor for,etc.) the control information at each period corresponding to theindicated periodicity. The control information may include UCI, CQI, andthe like. The base station may determine a quality (e.g., channelquality) associated with the active beam based on the controlinformation. Accordingly, the base station may determine whether theactive beam is satisfactory based on the control information.Alternatively, the base station may determine that the active beam isfailing and/or unsatisfactory based on the control information, and thebase station may determine that the active beam is to be changed. In thecontext of FIG. 7, the base station 702 may communicate, with the UE704, control information on a control channel through a beam of thebeams 720 a-h, such as the sixth beam 720 f when the fifth beam 720 e isthe active beam for communication between the base station 702 and theUE 704. In the context of FIG. 8, the base station 802 may communicate,with the UE 804, the information 844 on a control channel.

In one aspect, the base station may receive the control informationthrough the control-information beam, which may be a beam correspondingto a beam index included in a set of a candidate beam indexes. In thecontext of FIG. 8, the base station 802 may communicate, with the UE804, the information 844 on a control channel through thecontrol-information beam 820 f, and the beam index corresponding to thecontrol-information beam 820 f may be included in the set of candidatebeam indexes 830.

In another aspect, the base station may receive the control informationthrough the control-information beam, which may be a wide beam having anangle greater than that of the active beam. In the context of FIG. 8,the base station 802 may communicate, with the UE 804, the information844 on a control channel through the wide beam 822 (e.g., the wide beam822 may serve as the control-information beam).

In an aspect, operation 1406 may include operation 1420. In such anaspect, the control channel may be a PUCCH. At operation 1420, the basestation may receive, from the UE, the control information carried on thePUCCH through the control-information beam. In the context of FIG. 7,the base station 702 may receive, from the UE 704, control informationon a PUCCH through a beam of the beams 720 a-h, such as the sixth beam720 f when the fifth beam 720 e is the active beam for communicationbetween the base station 702 and the UE 704. In the context of FIG. 8,the base station 802 may receive, from the UE 804, the information 844on a PUCCH, for example, through the control-information beam 820 fand/or the wide beam 822.

At operation 1408, the base station may receive a request to change theactive beam. The request may indicate a beam index corresponding to asecond beam. In an aspect, the request indicates the beam index throughat least one of a cyclic shift and/or spreading across symbols. In anaspect, the request indicates the beam index through at least one of asubcarrier region (e.g., SR resources (e.g., region) of a subframe)and/or through RACH (e.g., RACH resources (e.g., region) of a subframe).

In the context of FIG. 7, the base station 702 may receive, from the UE704, the request 750, which may indicate a beam index corresponding to abeam of the beams 720 a-h. In the context of FIG. 8, the base station802, may receive, from the UE 804, a request, which may indicate a beamindex corresponding to another beam other than the current active beam820 e—e.g., the request may indicate the beam index corresponding to thecontrol-information beam 820 f, which may be a candidate beamcorresponding to a beam index included in a set of candidate beamindexes (e.g., the set of candidate beam indexes 830).

At operation 1410, the base station may change the active beam to thesecond beam that corresponds to the beam index indicated by the request.The base station may then communicate with the UE through the secondbeam, which may be the new active beam. In the context of FIG. 7, thebase station 702 may change the active beam to a beam of the beams 720a-h that corresponds to the beam index indicated by the request. In thecontext of FIG. 8, the base station 802, may change the active beam fromthe current active beam 820 e to a second beam corresponding to the beamindex indicated by the request—e.g., the base station 802 may change theactive beam to the control-information beam 820 f, which may be acandidate beam corresponding to a beam index included in a set ofcandidate beam indexes (e.g., the set of candidate beam indexes 830).

FIG. 15 is a flowchart of method 1500 of wireless communication. Themethod 1500 may be performed by a UE (e.g., the UE 704 and/or the UE804). In one aspect, the method 1500 may be performed by an apparatus.One of ordinary skill would understand that one or more operations maybe omitted, transposed, and or performed contemporaneously.

Beginning with operation 1502, the UE may communicate with a basestation through a first active beam. In an aspect, the communication maybe downlink communication. For example, the UE may receive data to fromthe base station. In an aspect, the communication may be uplinkcommunication. For example, the UE may determine a time (e.g., slot) atwhich the UE is scheduled to send data to the base station, and then theUE may transmit the data through the first active beam at the scheduledtime. In the context of FIG. 7, the UE 704 may communicate with the basestation 702 through a first active beam, such as the fifth beam 720 e.In the context of FIG. 8, the UE 804 may communicate with the basestation 802 through the active beam 820 e.

At operation 1504, the UE may receive, from the base station,information indicating a periodicity at which control information is tobe communicated on a control channel through a control-information beam.For example, the UE may receive, from the base station, information thatindicates the periodicity through the active beam. In the context ofFIG. 7, the UE 704 may receive, from the base station 702, informationindicating the periodicity through a current active beam, such as thefifth beam 720 e. In the context of FIG. 8, the base station 802 maytransmit, to the UE 804, the information 842 indicating the periodicitythrough the active beam 820 e.

In one aspect, the UE may receive the information indicating theperiodicity to the UE through RRC signaling. In another aspect, the UEmay receive the information indicating the periodicity on a PDCCH. Forexample, the information may be indicated by DCI of the PDCCH, such asone or more bits of one or more DCI formats that are reserved forinformation indicating the periodicity. Accordingly, the UE maydetermine the information based on the DCI of the PDCCH.

At operation 1506, the UE may communicate, with the base station, thecontrol information on the control channel through thecontrol-information beam at the periodicity. For example, the UE maytransmit the control information at each period corresponding to theindicated periodicity. In various aspects, the UE may measure a signalquality or channel estimate associated with communication with the basestation, e.g., through the active beam. For example, the UE may measurea signal quality (e.g., SNR, SINR, received power, received quality,etc.) for a signal (e.g., a BRS, a CSI-RS, a reference signal, etc.).The UE may generate a message to indicate the signal quality or channelestimate to the base station, and the UE may send the message to thebase station. In various aspects, the information may include UCI, CQI,SR, and/or other control information. In the context of FIG. 7, the UE704 may communicate, with the base station 702, control information on acontrol channel through a beam of the beams 720 a-h, such as the sixthbeam 720 f when the fifth beam 720 e is the active beam forcommunication between the base station 702 and the UE 704. In thecontext of FIG. 8, the base station 802 may communicate, with the UE804, the information 844 on a control channel.

In one aspect, the UE may send the control information through thecontrol-information beam, which may be a beam corresponding to a beamindex included in a set of a candidate beam indexes. In the context ofFIG. 8, the UE 804 may send, to the base station 802, the information844 on a control channel through the control-information beam 820 f, andthe beam index corresponding to the control-information beam 820 f.

In another aspect, the UE may send the control information through thecontrol-information beam, which may be a wide beam having an anglegreater than that of the active beam. In the context of FIG. 8, the UE804 may send, to the base station 802, the information 844 on a controlchannel through the wide beam 822 (e.g., the wide beam 822 may serve asthe control-information beam).

In an aspect, operation 1506 may include operation 1520. In such anaspect, the control channel may be a PUCCH. At operation 1520, the UEmay send, to the base station, the control information on the PUCCHthrough the control-information beam. In the context of FIG. 7, the UE704 may send, to the base station 702, control information on a PUCCHthrough a beam of the beams 720 a-h, such as the sixth beam 720 f whenthe fifth beam 720 e is the active beam for communication between thebase station 702 and the UE 704. In the context of FIG. 8, the UE 804may send, to the base station 802, the information 844 on a PUCCH, forexample, through the control-information beam 820 f and/or the wide beam822.

At operation 1508, the UE may send, to the base station, a request tochange the active beam. The request may indicate a beam indexcorresponding to a second beam. For example, the UE may determine thatthe active beam is failing and/or unsatisfactory based on the measuredsignal quality (e.g., based on comparison of the measured signal qualityto a threshold). Accordingly, the UE may request the base station tochange the active beam because the current active beam is failing and/orunsatisfactory. In an aspect, the request indicates the beam indexthrough at least one of a cyclic shift and/or spreading across symbols.In an aspect, the request indicates the beam index through at least oneof a subcarrier region (e.g., SR resources (e.g., region) of a subframe)and/or through RACH (e.g., RACH resources (e.g., region) of a subframe).

In the context of FIG. 7, the UE 704 may transmit, to the base station702, the request 750, which may indicate a beam index corresponding to abeam of the beams 720 a-h. In the context of FIG. 8, the UE 804 maytransmit, to the base station 802, a request, which may indicate a beamindex corresponding to another beam other than the current active beam820 e—e.g., the request may indicate the beam index corresponding to thecontrol-information beam 820 f, which may be a candidate beamcorresponding to a beam index included in a set of candidate beamindexes (e.g., the set of candidate beam indexes 830).

At operation 1510, the UE may change the active beam to the second beamthat corresponds to the beam index indicated by the request. The UE maythen communicate with the base station through the second beam, whichmay be the new active beam. In the context of FIG. 7, the UE 704 maychange the active beam to a beam of the beams 720 a-h that correspondsto the beam index indicated by the request. In the context of FIG. 8,the UE 804, may change the active beam from the current active beam 820e to a second beam corresponding to the beam index indicated by therequest—e.g., the UE 804 may change the active beam to thecontrol-information beam 820 f, which may be a candidate beamcorresponding to a beam index included in a set of candidate beamindexes (e.g., the set of candidate beam indexes 830).

FIG. 16 illustrates a flowchart 1600 of a method of wirelesscommunication. The method may be performed by a base station (e.g., thebase station 902) communicating with a UE (e.g., the UE 904). One ofordinary skill would understand that one or more operations may beomitted, transposed, and or performed contemporaneously.

At operation 1602, the base station may determine one or more indexesassociated with one or more beams. For example, the base station mayreceive BSI from the UE that includes one or more beam indexescorresponding to one or more beams of the base station. The base stationmay then identify a fine beam set based on BSI received from the UE. Inthe context of FIG. 9A-E, the base station 902 may determine one or moreindexes corresponding to the one or more beams 970, 972, 974.

At operation 1604, the base station may transmit, to a UE, one or moreindications of the one or more beam indexes. In various aspects, the oneor more indications may be carried on a control channel, such as aPDCCH. For example, the one or more indications may be indicated througha DCI message of the PDCCH. In the context of FIG. 9A-E, the basestation 902 may transmit the information 990 to the UE 904.

In an aspect, operation 1604 includes operations 1620 and 1622. Atoperation 1620, the base station may receive, from the UE, informationindicating one or more indexes corresponding to one or more beams. Inone aspect, the one or more indexes may be received from the UE througha PUSCH or a PUCCH. In one aspect, the information indicating the one ormore beam indexes may be one or more BSI reports. In the context of FIG.9A-E, the base station 902 may receive, from the UE 904, one or moreindexes associated with one or more beams.

At operation 1622, the base station may transmit one or more indexesbased on the one or more indexes that are most recently received fromthe UE. In one aspect, the base station may transmit one or more indexesbased on one or more indexes received from the UE through the PUSCH whenmore than two symbols are reserved for reference signal transmission. Inanother aspect, the base station may transmit one or more indexes basedon one or more indexes received from the UE through the PUCCH if one ortwo symbols are reserved for reference signal transmission. In thecontext of FIG. 9A-E, the base station 902 may transmit the information990 indicating the one or more indexes to the UE 904 based on the one ormore indexes that are most recently received from the UE 904.

In one aspect, operation 1604 may include operation 1624. At operation1624, the base station may transmit one or more indexes associated withone or more beam reference signals (e.g., one or more BRSs). The one ormore beam reference signals may be transmitted during a synchronizationsubframe. In the context of FIG. 9A-E, the base station 902 may transmitone or more indexes associated with one or more beam reference signals,which may be used for coarse beam training with the UE 904.

In one aspect, operation 1604 may include operation 1628. At operation1628, the base station may transmit one or more indexes corresponding toone or more beams that were transmitted during a previous referencesignal transmission (e.g., CSI-RS or BRRS transmission). In the contextof FIG. 9A-E, the base station 902 may transmit the information 990indicating the one or more beam indexes associated with one or morebeams that were transmitted during a previous reference signaltransmission to the UE 904.

At operation 1606, the base station may transmit, to the UE, a referencesignal based on the one or more Dis associated with the one or morebeams (e.g., as determined at operation 1602). In various aspects, thereference signal may be a CSI-RS, a BRRS, an MRS, or another referencesignal described herein. In the context of FIG. 9A-E, the base station902 may transmit, to the UE 904, one or more reference signals based onthe one or more indexes associated with the one or more beams.

FIG. 17 is a conceptual data flow diagram 1700 illustrating the dataflow between different means/components in an exemplary apparatus 1702.The apparatus may be a base station (e.g., the base station 602). Thedata flow illustrated in the diagram 1700 is to be regarded asillustrative. Therefore, one or more additional means/components may bepresent, and one or more illustrated means/components may be absent,according to various aspects. Further, various data flow may occurbetween means/components in addition to and/or instead of theillustrated data flow.

The apparatus 1702 may include a reception component 1704 configured toreceive signals from a UE (e.g., the UE 1750, a mmW UE, etc.). Theapparatus 1702 may further include a transmission component 1710configured to transmit signals to a UE (e.g., the UE 1750, a mmW UE,etc.).

The apparatus 1702 may include a communication component 1708. Thecommunication component 1708 may be configured to determine a beamcorresponding to a beam index. The communication component 1708 mayprovide an indication of the beam index to the reception component 1704so that the reception component 1704 may receive data from the UE 1750through the beam corresponding to the beam index. The communicationcomponent 1708 may provide an indication of the beam index to thetransmission component 1710 so that the transmission component 1710 maytransmit data to the UE 1750 through the beam corresponding to the beamindex. The beam through which the apparatus 1702 communicates with theUE 1750 may be an active beam.

In an aspect, the communication component 1708 may generate a referencesignal. The reference signal may be a CSI-RS, a CRS, an SSS, an MRS, aDMRS, or a BRS. The communication component 1708 may cause thetransmission component 1710 to transmit the reference signal to the UE1750 through a first active beam. In aspect, the communication component1708 may cause the reference signal to be transmitted through a firstRAT having a first carrier frequency (e.g., a 5G RAT, a mmW RAT, and/ora near-mmW RAT).

The apparatus 1702 may include a determination component 1712. Thedetermination component 1712 may be configured to determine that beamtracking is to be performed with the UE 1750. Beam tracking may includeselection or identification of an active beam through which theapparatus 1702 is to communicate with the UE 1750. The determinationcomponent 1712 may provide an indication that beam tracking is to beperformed to the beam tracking component 1706 in order to perform beamtracking.

In one aspect, the determination component 1712 may be configured todetermine a time at which the UE 1750 is to transition from an inactivecycle of DRX to an active cycle of DRX. The determination component 1712may determine that beam tracking is to be performed when the UE 1750transition to the active cycle of DRX. The determination component 1712may indicate, to the beam tracking component 1706, that beam tracking isto be performed with the UE 1750 at the time at which the UE 1750transition from the inactive cycle of DRX to the active cycle of DRX.

In one aspect, the determination component 1712 may be configured todetermine that beam tracking is to be performed with the UE 1750 basedon a response to the reference signal received from the UE 1750. In anaspect, the response may be received through a second RAT having adifferent carrier frequency than the first RAT—e.g., the second RAT mayhave a lower carrier frequency than the first RAT, and the second RATmay be a sub-6 GHz RAT and/or LTE RAT). In an aspect, the response mayinclude at least one of a CQI, an SINR, an SNR, an RSSI, a BRSRP, anRSRP, or an RSRQ. Thus, the response may indicate, to the determinationcomponent 1712, a signal quality. The determination component 1712 maycompare the signal quality to a threshold and determine that beamtracking is to be performed based on the comparison of the signalquality to the threshold.

In one aspect, the determination component 1712 may detect a radio linkfailure, for example, based on the response, an absence of the response,or at least one NACK message. The determination component 1712 maydetermine that beam tracking is to be performed based on the detectedradio link failure.

In one aspect, the determination component 1712 may determine an absenceof communication with the UE 1750 through the current active beam. Thedetermination component 1712 may determine that beam tracking is to beperformed based on the absence of communication. For example, thedetermination component 1712 may determine an absence of communicationusing a current active beam based on an absence of data carried on aPUCCH (e.g., when the UE 1750 is scheduled to communicate uplink data onthe PUCCH), an absence of data carried on a PUSCH (e.g., when the UE1750 is scheduled to communicate uplink data on the PUSCH), and/or anabsence of ACK/NACK messages from the UE 1750 (e.g., in response todownlink data communicated to the UE 1750).

In one aspect, the beam tracking component 1706 may perform beamtracking with the UE 1750. Beam tracking may allow the apparatus 1702 toselect or identify an active beam (e.g., a new beam) for communicationwith the UE 1750. In an aspect, the beam tracking component 1706 maycause the transmission component 1710 to transmit one or more BRSs(e.g., a coarse beam set). The beam tracking component 1706 may receive,through the reception component 1704, a first indication of a first beamindex based on one or more of the BRSs. The first beam index may be acoarse beam index. Based on the first beam index, the beam trackingcomponent 1706 may select or identify a fine set of beams through whichone or more BRRSs are to be transmitted, for example, for beamrefinement. The beam tracking component 1706 may select or identify thefine beam set as one or more beams that are proximate or close to thebeam corresponding to the first beam index. The beam tracking component1706 may then transmit one or more BRRSs through the fine set of beams.The beam tracking component 1706 may receive, through the receptioncomponent 1704, a second indication of a second beam index based on oneor more of the BRRSs. The second beam index may be a fine beam index.Based on the second beam index, the beam tracking component 1706 mayselect or identify a fine beam through the communication component 1708is to communicate with the UE 1750. The beam tracking component 1706 mayindicate, to the communication component 1708, the second beam index,which may be a new active beam for communication (e.g., uplink and/ordownlink communication) with the UE 1750.

In one aspect, the beam tracking component 1706 may receive, through thereception component 1704, a request to perform beam tracking (e.g., aBAR) from the UE 1750. Based on the request to perform beam tracking,the beam tracking component 1706 may select or identify a fine set ofbeams through which one or more BRRSs are to be transmitted, forexample, for beam refinement. The beam tracking component 1706 mayselect or identify the fine beam set as one or more beams that areproximate or close to a beam used for communication with the UE 1750(e.g., a most recent beam through which the apparatus 1702 communicatedwith the UE 1750). The beam tracking component 1706 may then transmitone or more BRRSs through the fine set of beams. The beam trackingcomponent 1706 may receive, through the reception component 1704, anindication of a beam index based on one or more of the BRRSs. The beamindex may be a fine beam index. Based on the beam index, the beamtracking component 1706 may select or identify a fine beam through thecommunication component 1708 is to communicate with the UE 1750. Thebeam tracking component 1706 may indicate, to the communicationcomponent 1708, the beam index, which may be a new active beam forcommunication (e.g., uplink and/or downlink communication) with the UE1750.

In an aspect, the beam tracking component 1706 may indicate, to the UE1750, that beam tracking is to be performed by causing transmission of amessage. For example, the beam tracking component 1706 may causetransmission of a message indicating that beam tracking is to beperformed, and the message may be carried on a PDCCH or a PDSCH. In anaspect, the message may be sent through DCI in the PDCCH.

The apparatus 1702 may include additional components that perform eachof the blocks of the algorithm in the aforementioned flowcharts of FIGS.10A, 10B, and/or 12. As such, each block in the aforementionedflowcharts of FIGS. 10A, 10B, and/or 12 may be performed by a componentand the apparatus 1702 may include one or more of those components. Thecomponents may be one or more hardware components specificallyconfigured to carry out the stated processes/algorithm, implemented by aprocessor configured to perform the stated processes/algorithm, storedwithin a computer-readable medium for implementation by a processor, orsome combination thereof.

FIG. 18 is a diagram 1800 illustrating an example of a hardwareimplementation for an apparatus 1702′ employing a processing system1814. The processing system 1814 may be implemented with a busarchitecture, represented generally by the bus 1824. The bus 1824 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 1814 and the overalldesign constraints. The bus 1824 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 1804, the components 1704, 1706, 1708, 1710, 1712 andthe computer-readable medium/memory 1806. The bus 1824 may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, and power management circuits, which are well known in theart, and therefore, will not be described any further.

The processing system 1814 may be coupled to a transceiver 1810. Thetransceiver 1810 is coupled to one or more antennas 1820. Thetransceiver 1810 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1810 receives asignal from the one or more antennas 1820, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1814, specifically the reception component 1704. Inaddition, the transceiver 1810 receives information from the processingsystem 1814, specifically the transmission component 1710, and based onthe received information, generates a signal to be applied to the one ormore antennas 1820. The processing system 1814 includes a processor 1804coupled to a computer-readable medium/memory 1806. The processor 1804 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 1806. The software, whenexecuted by the processor 1804, causes the processing system 1814 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 1806 may also be used forstoring data that is manipulated by the processor 1804 when executingsoftware. The processing system 1814 further includes at least one ofthe components 1704, 1706, 1708, 1710, 1712. The components may besoftware components running in the processor 1804, resident/stored inthe computer readable medium/memory 1806, one or more hardwarecomponents coupled to the processor 1804, or some combination thereof.The processing system 1814 may be a component of the base station 310and may include the memory 376 and/or at least one of the TX processor316, the RX processor 370, and the controller/processor 375.

In one configuration, the apparatus 1702/1702′ for wirelesscommunication includes means for communicating with a UE through a firstactive beam. The apparatus 1702/1702′ may further include means fordetermining that beam tracking is to be performed with the UE—the beamtracking including identifying a new beam for communication between theUE and the base station. The apparatus 1702/1702′ may further includemeans for performing beam tracking with the UE based on thedetermination that beam tracking is to be performed. The apparatus1702/1702′ may further include means for communicating with the UEthrough a second active beam based on the beam tracking.

In an aspect, the means for determining that beam tracking is to beperformed for the UE is configured to determine a time at which the UEis to transition from an inactive cycle of DRX to an active cycle ofDRX, and the means for performing the beam tracking is configured toperform the beam tracking based on the determined time.

In an aspect, the means for performing the beam tracking is configuredfor one or more of: transmission of at least one beam reference signal;reception, from the UE, of a first indication of a first beam indexbased on the beam reference signal; transmission, based on the firstindication of the first beam index, of at least one beam refinementreference signal; and reception, based on the at least one beamrefinement reference signal, of a second indication of a second beamindex, the second beam index corresponding to the second active beam.

In an aspect, the means for performing the beam tracking is configuredfor one or more of: reception, from the UE, of a request for beamtracking; transmission, based on the request for beam tracking, of atleast one beam refinement reference signal; and reception, based on theat least one beam refinement reference signal, of an indication of abeam index, the beam index corresponding to the second active beam.

In an aspect, the means for communicating with the UE through the firstactive beam is configured to send a reference signal to the UE todetermine if the first active beam is failing, and the means fordetermining that beam tracking is to be initiated for the UE isconfigured to receive a response from the UE based on the referencesignal; and detect a radio link failure based on the received response.

In an aspect, the communication with the UE through the first activebeam is performed with a first RAT, and the response is received througha second RAT, the second RAT having a lower carrier frequency than thefirst RAT. In an aspect, the reference signal is one of a CSI-RS, a CRS,an SSS, an MRS, a DMRS, or a BRS, and the response includes at least oneof a CQI, an SINR, an SNR, an RSSI, an RSRP, or a RSRQ.

In an aspect, the means for performing beam tracking with the UE isconfigured to send a message to the UE indicating that beam tracking isto be performed, and the message is sent on a PDCCH or a PDSCH. In anaspect, the message is sent through DCI in the PDCCH.

In an aspect, the means for determining that beam tracking is to beinitiated for the UE is configured to determine an absence ofcommunication with the UE through the first active beam. In an aspect,the determination of the absence of the communication with the UEthrough the first active beam is based on an absence of data carried ona PUCCH, an absence of data carried on a PUSCH, or an absence ofACK/NACK messages from the UE.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 1702 and/or the processing system 1814 ofthe apparatus 1702′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 1814 mayinclude the TX Processor 316, the RX Processor 370, and thecontroller/processor 375. As such, in one configuration, theaforementioned means may be the TX Processor 316, the RX Processor 370,and the controller/processor 375 configured to perform the functionsrecited by the aforementioned means.

FIG. 19 is a conceptual data flow diagram 1900 illustrating the dataflow between different means/components in an exemplary apparatus 1902.The apparatus may be a UE (e.g., the UE 604). The data flow illustratedin the diagram 1900 is to be regarded as illustrative. Therefore, one ormore additional means/components may be present, and one or moreillustrated means/components may be absent, according to variousaspects. Further, various data flow may occur between means/componentsin addition to the illustrated data flow.

The apparatus 1902 may include a reception component 1904 configured toreceive signals from a base station (e.g., the base station 1950, a mmWbase station, an eNB, etc.). The apparatus 1902 may further include atransmission component 1910 configured to transmit signals to a basestation (e.g., the base station 1950, a mmW base station, an eNB, etc.).

In an aspect, The apparatus 1902 may include a communication component1908. The communication component 1908 may be configured to determine abeam corresponding to a beam index, which may be a beam andcorresponding beam index at the base station 1950. The communicationcomponent 1908 may provide an indication of the beam index to thereception component 1904 so that the reception component 1904 mayreceive data from the base station 1950 through the beam correspondingto the beam index. The communication component 1908 may provide anindication of the beam index to the transmission component 1910 so thatthe transmission component 1910 may transmit data to the base station1950 through the beam corresponding to the beam index. The beam throughwhich the apparatus 1902 communicates with the base station 1950 may bean active beam.

In one aspect, the beam tracking component 1906 may perform beamtracking with the base station 1950. Beam tracking may allow theapparatus 1902 to select or identify an active beam (e.g., a new beam)for communication with the base station 1950. In an aspect, the beamtracking component 1906 may receive, through the reception component1904, one or more BRSs (e.g., a coarse beam set). The beam trackingcomponent 1906 may measure respective signal qualities for one or morereceived BRSs and may select a best beam corresponding to a best (e.g.,highest) signal quality for a received BRS. The beam tracking component1906 may transmit, through the transmission component 1910, a firstindication of a first beam index corresponding to the selected bestbeam. The first beam index may be a coarse beam index. Based on thefirst beam index, the beam tracking component 1906 may receive one ormore BRRSs, e.g., through a fine set of beams. The beam trackingcomponent 1906 may select a fine beam based on the one or more BRRSs(e.g., the beam tracking component may select a best beam based on abest or highest signal quality for a BRRS). The beam tracking component1906 may transmit, through the transmission component 1910, a secondindication of a second beam index corresponding to a BRRS having a bestor highest signal quality. The second beam index may be a fine beamindex. The beam tracking component 1906 may indicate, to thecommunication component 1908, the second beam index, which may be a newactive beam for communication (e.g., uplink and/or downlinkcommunication) with the base station 1950.

In one aspect, the beam tracking component 1906 may transmit, throughthe transmission component 1910, a request to perform beam tracking(e.g., a BAR). Based on the request for beam tracking, the beam trackingcomponent 1906 may receive one or more BRRSs, e.g., through a fine setof beams. The beam tracking component 1906 may select a fine beam basedon the one or more BRRSs (e.g., the beam tracking component may select abest beam based on a best or highest signal quality for a BRRS). Thebeam tracking component 1906 may transmit, through the transmissioncomponent 1910, an indication of a beam index corresponding to a BRRShaving a best or highest signal quality. The beam index may be a finebeam index. The beam tracking component 1906 may indicate, to thecommunication component 1908, the second beam index, which may be a newactive beam for communication (e.g., uplink and/or downlinkcommunication) with the base station 1950.

In an aspect, the beam tracking component 1906 may receive, from thebase station 1950, a message (e.g., signal) indicating that beamtracking is to be performed. For example, the beam tracking component1906 may receive, through the reception component 1904, a messageindicating that beam tracking is to be performed, and the message may becarried on a PDCCH or a PDSCH. In an aspect, the message may be receivedthrough DCI in the PDCCH.

The apparatus 1902 may include a determination component 1912. Thedetermination component 1912 may be configured to determine that beamtracking is to be performed with the base station 1950. Beam trackingmay include selection or identification of an active beam through whichthe apparatus 1902 is to communicate with the base station 1950. Thedetermination component 1912 may provide an indication that beamtracking is to be performed to the beam tracking component 1906 in orderto perform beam tracking.

In one aspect, the determination component 1912 may be configured toreceive, through the reception component 1904, a signal associated withbeam tracking. In one aspect, the signal may be a BRS or BRRS. Inanother aspect, the signal may be a reference signal. The referencesignal may be one of a CSI-RS, a CRS, an SSS, an MRS, a DMRS, or thelike.

In one aspect, the determination component 1912 may be configured tocause the transmission component 1910 to transmit a response to thereference signal. In various aspects, the response may include one of aCQI, an SINR, an SNR, an RSSI, a BRSRP, an RSRP, or an RSRQ. Forexample, the determination component 1912 may measure a signal quality(e.g., an SINR, an SNR, an RSSI, a BRSRP, an RSRP, an RSRQ, etc.) basedon the reference signal. The determination component 1912 may generate aresponse that includes the measured signal quality.

In an aspect, the determination component 1912 may receive the signalthrough a first RAT (e.g., a 5G RAT, a mmW RAT, a near-mmW RAT, etc.).However, the determination component 1912 may cause transmission of theresponse through a second RAT having a different carrier frequency thanthe first RAT—e.g., the second RAT may have a lower carrier frequencythan the first RAT, and the second RAT may be a sub-6 GHz RAT and/or LTERAT.

In one aspect, the determination component 1912 may detect a radio linkfailure, for example, based on the signal (e.g., reference signal). Forexample, the determination component 1912 may measure a signal qualityof the reference signal. The determination component 1912 may comparethe signal quality to a threshold and detect a radio link failure basedon comparison of the measured signal quality to the threshold. Thedetermination component 1912 may determine that beam tracking is to beperformed based on the detected radio link failure. The determinationcomponent 1912 may cause the transmission component 1910 to transmit, tothe base station 1950, an indication of the detected radio link failureand/or the determination component 1912 may indicate to the beamtracking component 1906 that beam tracking is to be performed, forexample, to recover an active beam for communication.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIGS. 11A,11B, and/or 13. As such, each block in the aforementioned flowcharts ofFIGS. 11A, 11B, and/or 13 may be performed by a component and theapparatus 1902 may include one or more of those components. Thecomponents may be one or more hardware components specificallyconfigured to carry out the stated processes/algorithm, implemented by aprocessor configured to perform the stated processes/algorithm, storedwithin a computer-readable medium for implementation by a processor, orsome combination thereof.

FIG. 20 is a diagram 2000 illustrating an example of a hardwareimplementation for an apparatus 1902′ employing a processing system2014. The processing system 2014 may be implemented with a busarchitecture, represented generally by the bus 2024. The bus 2024 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 2014 and the overalldesign constraints. The bus 2024 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 2004, the components 1904, 1906, 1908, 1910, 1912, andthe computer-readable medium/memory 2006. The bus 2024 may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, and power management circuits, which are well known in theart, and therefore, will not be described any further.

The processing system 2014 may be coupled to a transceiver 2010. Thetransceiver 2010 is coupled to one or more antennas 2020. Thetransceiver 2010 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 2010 receives asignal from the one or more antennas 2020, extracts information from thereceived signal, and provides the extracted information to theprocessing system 2014, specifically the reception component 1904. Inaddition, the transceiver 2010 receives information from the processingsystem 2014, specifically the transmission component 1910, and based onthe received information, generates a signal to be applied to the one ormore antennas 2020. The processing system 2014 includes a processor 2004coupled to a computer-readable medium/memory 2006. The processor 2004 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 2006. The software, whenexecuted by the processor 2004, causes the processing system 2014 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 2006 may also be used forstoring data that is manipulated by the processor 2004 when executingsoftware. The processing system 2014 further includes at least one ofthe components 1904, 1906, 1908, 1910, 1912. The components may besoftware components running in the processor 2004, resident/stored inthe computer readable medium/memory 2006, one or more hardwarecomponents coupled to the processor 2004, or some combination thereof.The processing system 2014 may be a component of the UE 350 and mayinclude the memory 360 and/or at least one of the TX processor 368, theRX processor 356, and the controller/processor 359.

In one configuration, the apparatus 1902/1902′ for wirelesscommunication includes means for communicating with a base stationthrough a first active beam. The apparatus 1902/1902′ may furtherinclude means for receiving a signal from the base station associatedwith beam tracking, the beam tracking including identifying a new beamfor communication between the apparatus 1902/1902′ and the base station.The apparatus 1902/1902′ may further include means for communicatingwith the base station through a second active beam based on the signalassociated with beam tracking.

In an aspect, the signal includes a BRRS, and the apparatus 1902/1902′further includes means for sending, to the base station, a beam indexcorresponding to the second active beam based on the BRRS. In an aspect,the signal includes a BRS, and the apparatus 1902/1902′ further includesmeans for sending, to the base station, a beam index corresponding to acoarse beam. In an aspect, the apparatus 1902/1902′ may further includesmeans for sending, to the base station, a request to perform beamtracking based on the signal.

In an aspect, the means for communicating with the base station throughthe first active beam is configured to receive a reference signal, andthe apparatus 1902/1902′ further includes means for detecting a radiolink failure based on the reception of the reference signal and meansfor sending an indication to the base station based on the detectedradio link failure. In an aspect, the reference signal is one of aCSI-RS, a CRS, an SSS, an MRS, a DMRS, or a BRS, and the indicationincludes at least one of a CQI, an SINR, an SNR, an RSSI, an RSRP, or anRSRQ. In an aspect, the means for communicating with the base stationthrough the first active beam is performed with a first RAT, and themeans for sending the indication is configured to send the indicationthrough a second RAT, the first RAT having a higher carrier frequencythan the second RAT.

In an aspect, the apparatus 1902/1902′ further includes means forperforming beam tracking with the base station. In an aspect, the meansfor performing the beam tracking is configured for one or more of:reception, from the base station, of at least one BRS; transmission, tothe base station, of a first indication of a first beam index based onthe BRS; reception of at least one BRRS; and transmission, based on theat least one BRRS, of a second indication of a second beam index.

In an aspect, the signal is received on a PDCCH or a PDSCH. In anaspect, the signal is received through DCI on the PDCCH.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 1902 and/or the processing system 2014 ofthe apparatus 1902′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 2014 mayinclude the TX Processor 368, the RX Processor 356, and thecontroller/processor 359. As such, in one configuration, theaforementioned means may be the TX Processor 368, the RX Processor 356,and the controller/processor 359 configured to perform the functionsrecited by the aforementioned means.

FIG. 21 is a conceptual data flow diagram 2100 illustrating the dataflow between different means/components in an exemplary apparatus 2102.The apparatus may be a base station (e.g., the base station 702, thebase station 802, etc.). The data flow illustrated in the diagram 2100is to be regarded as illustrative. Therefore, one or more additionalmeans/components may be present, and one or more illustratedmeans/components may be absent, according to various aspects. Further,various data flow may occur between means/components in addition toand/or instead of the illustrated data flow.

The apparatus 2102 may include a reception component 2104 configured toreceive signals from a UE (e.g., the UE 2150, a mmW UE, etc.). Theapparatus 2102 may further include a transmission component 2110configured to transmit signals to a UE (e.g., the UE 2150, a mmW UE,etc.).

The apparatus 2102 may include a communication component 2108. Thecommunication component 2108 may be configured to determine a beamcorresponding to a beam index. The communication component 2108 mayprovide an indication of the beam index to the reception component 2104so that the reception component 2104 may receive data from the UE 2150through the beam corresponding to the beam index. The communicationcomponent 2108 may provide an indication of the beam index to thetransmission component 2110 so that the transmission component 2110 maytransmit data to the UE 2150 through the beam corresponding to the beamindex. The beam through which the apparatus 2102 communicates with theUE 2150 may be an active beam.

In an aspect, the apparatus 2102 may include a control component 2112.The control component 2112 may be configured to determine a periodicityat which control information is to be communicated on a control channelthrough a control-information beam. In an aspect, the control component2112 may cause the transmission component to transmit informationindicating the periodicity to the UE. In one aspect, the controlcomponent 2112 may cause transmission of the information indicating theperiodicity through RRC signaling. In another aspect, the controlcomponent 2112 may cause transmission of the information indicating theperiodicity on a PDDCH. For example, the control component 2112 maycause transmission of the information indicating the periodicity as DCIof the PDCCH.

In an aspect, the control component 2112 may communicate, with the UE,the control information on the control channel through acontrol-information beam at the periodicity. The control-informationbeam may be different than the active beam. In an aspect, thecontrol-information beam includes at least one candidate beamcorresponding to a beam index included in a set of candidate beamindexes. In an aspect, the control-information beam includes at leastone wide beam, which may have an angle greater than that of the activebeam.

In an aspect, the control channel may include a PUCCH. The controlcomponent 2112 may be configured to receive, through the receptioncomponent, the control information carried on a PUCCH through thecontrol-information beam based on the periodicity.

The apparatus 2102 may include a beam switching component 2106 forswitching or changing the active beam. The beam switching component 2106may receive, through the reception component 2104, a request to changethe active beam. The request may indicate a beam index corresponding toa second beam. For example, the request may indicate the beam indexthrough at least one of a cyclic shift or spreading across symbols. Inanother example, the request may indicate the beam index through atleast one of a subcarrier region or a RACH. The beam switching component2106 may determine the second beam based on the request and provide thebeam index to the communication component 2108 for communication throughthe new active beam.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIG. 14. Assuch, each block in the aforementioned flowcharts of FIG. 14 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 22 is a diagram 2200 illustrating an example of a hardwareimplementation for an apparatus 2102′ employing a processing system2214. The processing system 2214 may be implemented with a busarchitecture, represented generally by the bus 2224. The bus 2224 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 2214 and the overalldesign constraints. The bus 2224 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 2204, the components 2104, 2106, 2108, 2110, 2112 andthe computer-readable medium/memory 2206. The bus 2224 may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, and power management circuits, which are well known in theart, and therefore, will not be described any further.

The processing system 2214 may be coupled to a transceiver 2210. Thetransceiver 2210 is coupled to one or more antennas 2220. Thetransceiver 2210 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 2210 receives asignal from the one or more antennas 2220, extracts information from thereceived signal, and provides the extracted information to theprocessing system 2214, specifically the reception component 2104. Inaddition, the transceiver 2210 receives information from the processingsystem 2214, specifically the transmission component 2110, and based onthe received information, generates a signal to be applied to the one ormore antennas 2220. The processing system 2214 includes a processor 2204coupled to a computer-readable medium/memory 2206. The processor 2204 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 2206. The software, whenexecuted by the processor 2204, causes the processing system 2214 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 2206 may also be used forstoring data that is manipulated by the processor 2204 when executingsoftware. The processing system 2214 further includes at least one ofthe components 2104, 2106, 2108, 2110, 2112. The components may besoftware components running in the processor 2204, resident/stored inthe computer readable medium/memory 2206, one or more hardwarecomponents coupled to the processor 2204, or some combination thereof.The processing system 2214 may be a component of the base station 310and may include the memory 376 and/or at least one of the TX processor316, the RX processor 370, and the controller/processor 375.

In one configuration, the apparatus 2102/2102′ for wirelesscommunication includes means for communicating with a UE through anactive beam. The apparatus 2102/2102′ further includes means fortransmitting, to the UE, information indicating a periodicity at whichcontrol information is to be communicated on a control channel through acontrol-information beam. The apparatus 2102/2102′ further includesmeans for communicating, with the UE, the control information on thecontrol channel through the control-information beam at the periodicity.

In an aspect, the control channel includes a PUCCH, and the means forcommunicating, with the UE, the control information on the controlchannel is configured to receive, from the UE, the control informationcarried on the PUCCH through the control-information beam based on theperiodicity.

In an aspect, the control-information beam includes at least onecandidate beam, the at least one candidate beam corresponding to a beamindex included in a set of candidate beam indexes maintained by the basestation. In an aspect, the control-information beam includes at leastone wide beam, the at least one wide beam having an angle greater thanthat of the active beam.

In an aspect, the information indicating the periodicity is transmittedthrough RRC signaling. In an aspect, the information indicating theperiodicity is transmitted on a PDCCH. In an aspect, the informationindicating the periodicity includes DCI of the PDCCH.

In an aspect, the apparatus 2102/2102′ may further include means forreceiving a request to change the active beam, the request indicating abeam index corresponding to a second beam. In an aspect, the apparatus2102/2102′ may further include means for changing the active beam to thesecond beam corresponding to the beam index indicated by the request. Inan aspect, the request indicates the beam index through at least one ofa cyclic shift or spreading across symbols. In an aspect, the requestindicates the beam index through at least one of a subcarrier region ora RACH.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 2102 and/or the processing system 2214 ofthe apparatus 2102′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 2214 mayinclude the TX Processor 316, the RX Processor 370, and thecontroller/processor 375. As such, in one configuration, theaforementioned means may be the TX Processor 316, the RX Processor 370,and the controller/processor 375 configured to perform the functionsrecited by the aforementioned means.

FIG. 23 is a conceptual data flow diagram 2300 illustrating the dataflow between different means/components in an exemplary apparatus 2302.The apparatus may be a UE (e.g., the UE 704, the UE 804, etc.). The dataflow illustrated in the diagram 2300 is to be regarded as illustrative.Therefore, one or more additional means/components may be present, andone or more illustrated means/components may be absent, according tovarious aspects. Further, various data flow may occur betweenmeans/components in addition to the illustrated data flow.

The apparatus 2302 may include a reception component 2304 configured toreceive signals from a base station (e.g., the base station 2350, a mmWbase station, an eNB, etc.). The apparatus 2302 may further include atransmission component 2310 configured to transmit signals to a basestation (e.g., the base station 2350, a mmW base station, an eNB, etc.).

In an aspect, The apparatus 2302 may include a communication component2308. The communication component 2308 may be configured to determine abeam corresponding to a beam index, which may be a beam andcorresponding beam index at the base station 2350. The communicationcomponent 2308 may provide an indication of the beam index to thereception component 2304 so that the reception component 2304 mayreceive data from the base station 2350 through the beam correspondingto the beam index. The communication component 2308 may provide anindication of the beam index to the transmission component 2310 so thatthe transmission component 2310 may transmit data to the base station2350 through the beam corresponding to the beam index. The beam throughwhich the apparatus 2302 communicates with the base station 2350 may bean active beam.

In an aspect, the apparatus 2302 may include a control component 2312.The control component 2312 may be configured to determine a periodicityat which control information is to be communicated on a control channelthrough a control-information beam. In an aspect, the control component2312 may receive, through the reception component 2304, the transmissioncomponent to transmit information indicating the periodicity from thebase station 2350. The control component 2312 may determine theperiodicity based on the information indicating the periodicity. In oneaspect, the control component 2312 may receive the informationindicating the periodicity through RRC signaling. In another aspect, thecontrol component 2312 may receive the information indicating theperiodicity on a PDDCH. For example, the control component 2312 mayreceive the information indicating the periodicity as DCI of the PDCCH.

In an aspect, the control component 2312 may communicate, with the basestation 2350, the control information on the control channel through acontrol-information beam at the periodicity. The control-informationbeam may be different than the active beam. In an aspect, thecontrol-information beam includes at least one candidate beamcorresponding to a beam index included in a set of candidate beamindexes. In an aspect, the control-information beam includes at leastone wide beam, which may have an angle greater than that of the activebeam.

In an aspect, the control channel may include a PUCCH. The controlcomponent 2312 may be configured to send, to the base station 2350, thecontrol information through the control-information beam based on theperiodicity.

The apparatus 2302 may include a beam switching component 2306 forswitching or changing the active beam. The beam switching component 2306may send, through the transmission component 2310, a request to changethe active beam. The request may indicate a beam index corresponding toa second beam. For example, the request may indicate the beam indexthrough at least one of a cyclic shift or spreading across symbols. Inanother example, the request may indicate the beam index through atleast one of a subcarrier region or a RACH. The beam switching component2306 may provide the beam index to the communication component 2308 forcommunication through the new active beam, which may match the activebeam at the base station 2350 after transmission of the request.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIG. 15. Assuch, each block in the aforementioned flowcharts of FIG. 15 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 24 is a diagram 2400 illustrating an example of a hardwareimplementation for an apparatus 2302′ employing a processing system2414. The processing system 2414 may be implemented with a busarchitecture, represented generally by the bus 2424. The bus 2424 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 2414 and the overalldesign constraints. The bus 2424 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 2404, the components 2304, 2306, 2308, 2310, 2312 andthe computer-readable medium/memory 2406. The bus 2424 may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, and power management circuits, which are well known in theart, and therefore, will not be described any further.

The processing system 2414 may be coupled to a transceiver 2410. Thetransceiver 2410 is coupled to one or more antennas 2420. Thetransceiver 2410 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 2410 receives asignal from the one or more antennas 2420, extracts information from thereceived signal, and provides the extracted information to theprocessing system 2414, specifically the reception component 2304. Inaddition, the transceiver 2410 receives information from the processingsystem 2414, specifically the transmission component 2310, and based onthe received information, generates a signal to be applied to the one ormore antennas 2420. The processing system 2414 includes a processor 2404coupled to a computer-readable medium/memory 2406. The processor 2404 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 2406. The software, whenexecuted by the processor 2404, causes the processing system 2414 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 2406 may also be used forstoring data that is manipulated by the processor 2404 when executingsoftware. The processing system 2414 further includes at least one ofthe components 2304, 2306, 2308, 2310, 2312. The components may besoftware components running in the processor 2404, resident/stored inthe computer readable medium/memory 2406, one or more hardwarecomponents coupled to the processor 2404, or some combination thereof.The processing system 2414 may be a component of the UE 350 and mayinclude the memory 360 and/or at least one of the TX processor 368, theRX processor 356, and the controller/processor 359.

In one configuration, the apparatus 2302/2302′ for wirelesscommunication includes means for communicating with a base stationthrough an active beam. In an aspect, the apparatus 2302/2302′ furtherincludes means for receiving, from the base station, informationindicating a periodicity at which control information is to becommunicated on a control channel through a control-information beam. Inan aspect, the apparatus 2302/2302′ further includes means forcommunicating, with the base station, the control information on thecontrol channel through the control-information beam at the periodicity.

In an aspect, the control channel includes a PUCCH, and the means forcommunicating the control information on the control channel isconfigured to send, to the base station, the control information on thePUCCH through the control-information beam based on the periodicity.

In an aspect, the control-information beam includes at least onecandidate beam, the at least one candidate beam corresponding to a beamindex included in a set of candidate beam indexes. In an aspect, thecontrol-information beam includes at least one wide beam, the at leastone wide beam having an angle greater than that of the active beam. Inan aspect, the information indicating the periodicity is received usingRRC signaling. In an aspect, the information indicating the periodicityis received on a PDCCH. In an aspect, the information indicating theperiodicity is indicated by DCI of the PDCCH.

In an aspect, the apparatus 2302/2302′ further includes means fortransmitting, to the base station, a request to change the active beam,the request indicating a beam index corresponding to a second beam. Inan aspect, the apparatus 2302/2302′ further includes means for changingthe active beam to the second beam corresponding to the beam indexindicated by the request. In an aspect, the request indicates the beamindex through at least one of a cyclic shift or spreading acrosssymbols. In an aspect, the request indicates the beam index through atleast one of a subcarrier region or a RACH.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 2302 and/or the processing system 2414 ofthe apparatus 2302′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 2414 mayinclude the TX Processor 368, the RX Processor 356, and thecontroller/processor 359. As such, in one configuration, theaforementioned means may be the TX Processor 368, the RX Processor 356,and the controller/processor 359 configured to perform the functionsrecited by the aforementioned means.

FIG. 25 is a conceptual data flow diagram 2500 illustrating the dataflow between different means/components in an exemplary apparatus 2502.The apparatus may be a base station (e.g., the base station 902, etc.).The data flow illustrated in the diagram 2500 is to be regarded asillustrative. Therefore, one or more additional means/components may bepresent, and one or more illustrated means/components may be absent,according to various aspects. Further, various data flow may occurbetween means/components in addition to and/or instead of theillustrated data flow.

The apparatus 2502 may include a reception component 2504 configured toreceive signals from a UE (e.g., the UE 2550, a mmW UE, etc.). Theapparatus 2502 may further include a transmission component 2510configured to transmit signals to a UE (e.g., the UE 2550, a mmW UE,etc.).

In aspects, the apparatus 2502 may include a determination component2512. The determination component 2512 may be configured to determineone or more beam indexes corresponding to one or more beams of theapparatus 2502 through which one or more reference signals are to betransmitted. For example, the determination component 2512 may receive,through the reception component 2504, one or more beam indexes from theUE 2550. The beam indexes may be based on one or more reference signalspreviously sent be the apparatus 2502, such as one or more BRSs, BRRSs,CSI-RSs, or another reference signal.

In one aspect, the one or more beam indexes are received from the UE2550 in one or more BSI reports. In one aspect, the one or more beamindexes corresponding to the one or more beams are received on a PUSCHor a PUCCH. The one or more beam indexes corresponding to the one ormore beams may be received on a PUSCH when more than two symbols arereserved for reference signal transmission. The one or more beam indexescorresponding to the one or more beams may be received on a PUCCH whentwo or fewer symbols are reserved for reference signal transmission.

In one aspect, the determination component 2512 may determine the one ormore beam indexes based on one more beam indexes that are most recentlyreceived form the UE 2550. In one aspect, the determination component2512 may determine the one or more beam indexes based on transmittingone or more BRSs during a synchronization subframe. The determinationcomponent 2512 may reuse the beams one which the one or more BRSs aretransmitted, for example, based on feedback from the UE 2550 indicatingthe best beam indexes corresponding to the best beams (e.g., the beam(s)through an associated BRS is transmitted, and the BRS has a highestmeasured signal quality).

The determination component 2512 may provide an indication of the one ormore beam indexes corresponding to the one or more beams to anindication component 2506. The indication component 2506 may beconfigured to generate one or more indications of the one or more beamindexes corresponding to the one or more beams. The indication component2506 may then cause the transmission component 2510 to transmit the oneor more indications to the UE 2550. In one aspect, the one or moreindications may be carried on a PDCCH. For example, the one or moreindications may be included in one or more bits of a DCI message of aPDCCH.

The determination component 2512 may provide an indication of the one ormore beam indexes corresponding to the one or more beams to a referencesignal component 2508. The reference signal component 2508 may beconfigured to generate one or more reference signals. A generatedreference signal may be at least one of a BRRS or a CSI-RS. Thereference signal component 2508 may then cause the transmissioncomponent 2510 to transmit the one or more reference signals through theone or more beams corresponding to the one or more beam indexes, whichwere send to the UE 2550 by the indication component 2506.

The apparatus may include additional components that perform each of theblocks of the algorithm in the aforementioned flowcharts of FIG. 16. Assuch, each block in the aforementioned flowcharts of FIG. 16 may beperformed by a component and the apparatus may include one or more ofthose components. The components may be one or more hardware componentsspecifically configured to carry out the stated processes/algorithm,implemented by a processor configured to perform the statedprocesses/algorithm, stored within a computer-readable medium forimplementation by a processor, or some combination thereof.

FIG. 26 is a diagram 2600 illustrating an example of a hardwareimplementation for an apparatus 2502′ employing a processing system2614. The processing system 2614 may be implemented with a busarchitecture, represented generally by the bus 2624. The bus 2624 mayinclude any number of interconnecting buses and bridges depending on thespecific application of the processing system 2614 and the overalldesign constraints. The bus 2624 links together various circuitsincluding one or more processors and/or hardware components, representedby the processor 2604, the components 2504, 2506, 2508, 2510, 2512 andthe computer-readable medium/memory 2606. The bus 2624 may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, and power management circuits, which are well known in theart, and therefore, will not be described any further.

The processing system 2614 may be coupled to a transceiver 2610. Thetransceiver 2610 is coupled to one or more antennas 2620. Thetransceiver 2610 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 2610 receives asignal from the one or more antennas 2620, extracts information from thereceived signal, and provides the extracted information to theprocessing system 2614, specifically the reception component 2504. Inaddition, the transceiver 2610 receives information from the processingsystem 2614, specifically the transmission component 2510, and based onthe received information, generates a signal to be applied to the one ormore antennas 2620. The processing system 2614 includes a processor 2604coupled to a computer-readable medium/memory 2606. The processor 2604 isresponsible for general processing, including the execution of softwarestored on the computer-readable medium/memory 2606. The software, whenexecuted by the processor 2604, causes the processing system 2614 toperform the various functions described supra for any particularapparatus. The computer-readable medium/memory 2606 may also be used forstoring data that is manipulated by the processor 2604 when executingsoftware. The processing system 2614 further includes at least one ofthe components 2504, 2506, 2508, 2510, 2512. The components may besoftware components running in the processor 2604, resident/stored inthe computer readable medium/memory 2606, one or more hardwarecomponents coupled to the processor 2604, or some combination thereof.The processing system 2614 may be a component of the base station 310and may include the memory 376 and/or at least one of the TX processor316, the RX processor 370, and the controller/processor 375.

In one configuration, the apparatus 2502/2502′ for wirelesscommunication includes means for transmitting, to a UE on a controlchannel, one or more indications of one or more beam indexescorresponding to one or more beams. The apparatus 2502/2502′ may furtherinclude means for transmitting, to the UE, one or more reference signalsthrough the one or more beams corresponding to the one or more beamindexes. In an aspect, the control channel comprises a PDCCH, and theone or more indications are included in one or more bits of a DCImessage.

In an aspect, the means for transmitting the one or more indications ofthe one or more beam indexes corresponding to the one or more beams isconfigured to transmit one or more beam indexes associated with one ormore BRSs, the one or more BRSs transmitted during a synchronizationsubframe.

In an aspect, the means for transmitting the one or more indications ofthe one or more beam indexes corresponding to the one or beams isconfigured to: receive, from the UE, one or more beam indexescorresponding to the one or more beams; and transmit the one or morebeam indexes corresponding to the one or more beams based on the one ormore beam indexes that are received most recently.

In an aspect, the one or more beam indexes corresponding to the one ormore beams are received on a PUSCH or a PUCCH. In an aspect, the one ormore beam indexes corresponding to the one or more beams are transmittedbased on the one or more beam indexes received through the PUSCH whenmore than two symbols are used for the reference signal transmission. Inan aspect, the one or more beam indexes associated with one or morebeams are transmitted based on the one or more beam indexes receivedthrough the PUCCH when two or fewer symbols are used for the referencesignal transmission.

In an aspect, the one or more reference signals include at least one ofa CSI-RS or a BRRS. In an aspect, the means for transmitting the one ormore indications of the one or more beam indexes associated with the oneor more beams is configured to transmit the one or more beam indexesassociated with the one or more beams through which at least one of theCSI-RSs was previously transmitted.

The aforementioned means may be one or more of the aforementionedcomponents of the apparatus 2502 and/or the processing system 2614 ofthe apparatus 2502′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 2614 mayinclude the TX Processor 316, the RX Processor 370, and thecontroller/processor 375. As such, in one configuration, theaforementioned means may be the TX Processor 316, the RX Processor 370,and the controller/processor 375 configured to perform the functionsrecited by the aforementioned means.

It is understood that the specific order or hierarchy of blocks in theprocesses/flowcharts disclosed is an illustration of exemplaryapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flowcharts may berearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “one or more of A, B, or C,” “at least oneof A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or anycombination thereof” include any combination of A, B, and/or C, and mayinclude multiples of A, multiples of B, or multiples of C. Specifically,combinations such as “at least one of A, B, or C,” “one or more of A, B,or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and“A, B, C, or any combination thereof” may be A only, B only, C only, Aand B, A and C, B and C, or A and B and C, where any such combinationsmay contain one or more member or members of A, B, or C. All structuraland functional equivalents to the elements of the various aspectsdescribed throughout this disclosure that are known or later come to beknown to those of ordinary skill in the art are expressly incorporatedherein by reference and are intended to be encompassed by the claims.Moreover, nothing disclosed herein is intended to be dedicated to thepublic regardless of whether such disclosure is explicitly recited inthe claims. The words “module,” “mechanism,” “element,” “device,” andthe like may not be a substitute for the word “means.” As such, no claimelement is to be construed as a means plus function unless the elementis expressly recited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication for a userequipment (UE), the method comprising: sending, to a base station in afirst carrier frequency, a request associated with performance of beamtracking between the base station and the UE in a second carrierfrequency that is different from the first carrier frequency;performing, based on the request, the beam tracking with the basestation to determine a communication beam, wherein the performing thebeam tracking comprises: receiving a plurality of reference signals fromthe base station, wherein each of the plurality of reference signals isreceived via a respective beam of a plurality of beams, and sending, tothe base station in the second carrier frequency, information indicatingat least one beam index corresponding to at least one beam of theplurality of beams based on a plurality of measurements associated withreceiving the plurality of reference signals, wherein each measurementof the plurality of measurements is associated with a respective beam ofthe plurality of beams; and communicating with the base station on thecommunication beam in the second carrier frequency based on the beamtracking.
 2. The method of claim 1, wherein the first carrier frequencycomprises a sub-6 gigahertz (GHz) band and the second carrier frequencycomprises a millimeter wave (mmW) band.
 3. The method of claim 1,wherein the first carrier frequency is associated with a first radioaccess technology (RAT) and the second carrier frequency is associatedwith a second RAT that is different from the first RAT.
 4. The method ofclaim 1, wherein the request indicates a beam index associated with theat least one first beam.
 5. The method of claim 4, wherein the requestindicates the beam index associated with the at least one first beambased on one or more resources associated with a random access channel(RACH).
 6. The method of claim 1, wherein at least one second referencesignal of the plurality of reference signals is received on at least onesecond beam of the plurality of beams based on the first indication ofthe first beam index.
 7. The method of claim 1, further comprising:detecting a radio link failure associated with communication with thebase station on a serving beam in the second carrier frequency, whereinthe sending the request is based on the radio link failure.
 8. Themethod of claim 7, wherein the detecting the radio link failurecomprises: measuring a value associated with the serving beam, whereinthe value comprises at least one of a signal-to-noise ratio (SNR), asignal-to-interference-plus-noise ratio (SINR), a received signalstrength indicator (RSSI), a reference signal received quality, or areference signal received power (RSRP); comparing the value to athreshold; and detecting the radio link failure based on the comparisonof the value to the threshold.
 9. A method of wireless communication fora base station, the method comprising: receiving, from a user equipment(UE) in a first carrier frequency, a request associated with performanceof beam tracking between the base station and the UE in a second carrierfrequency that is different from the first carrier frequency;performing, based on the request, the beam tracking with the UE todetermine a communication beam, wherein the performing the beam trackingcomprises: sending a plurality of reference signals, wherein each of theplurality of reference signals is sent via a respective beam of aplurality of beams, and receiving, from the UE in the second carrierfrequency, information indicating at least one beam index correspondingto at least one beam of the plurality of beams based on a plurality ofmeasurements associated with receiving the plurality of referencesignals by the UE, wherein each measurement of the plurality ofmeasurements is associated with a respective beam of the plurality ofbeams; and communicating with the UE on the communication beam in thesecond carrier frequency based on the beam tracking.
 10. The method ofclaim 9, wherein the first carrier frequency comprises a sub-6 gigahertz(GHz) band and the second carrier frequency comprises a millimeter wave(mmW) band.
 11. The method of claim 9, wherein the first carrierfrequency is associated with a first radio access technology (RAT) andthe second carrier frequency is associated with a second RAT that isdifferent from the first RAT.
 12. The method of claim 9, wherein therequest indicates a beam index associated with the at least one firstbeam.
 13. The method of claim 12, wherein the request indicates the beamindex associated with the at least one first beam based on one or moreresources associated with a random access channel (RACH).
 14. The methodof claim 9, wherein at least one second reference signal of theplurality of reference signals is sent on at least one second beam ofthe plurality of beams based on the first indication of the first beamindex.
 15. The method of claim 9, wherein the request is based on aradio link failure between the base station and the UE on a servingbeam.
 16. A method of wireless communication for a user equipment (UE),the method comprising: receiving, from a base station in a first carrierfrequency, a message indicating an instruction to perform beam trackingbetween the base station and the UE in a second carrier frequency thatis different from the first carrier frequency; performing, based on theinstruction, the beam tracking with the base station to determine acommunication beam, wherein the performing the beam tracking comprises:receiving a plurality of reference signals from the base station,wherein each of the plurality of reference signals is received via arespective beam of a plurality of beams, and sending, to the basestation in the second carrier frequency, information indicating at leastone beam index corresponding to at least one beam of the plurality ofbeams based on a plurality of measurements associated with receiving theplurality of reference signals, wherein each measurement of theplurality of measurements is associated with a respective beam of theplurality of beams; and communicating with the base station on thecommunication beam in the second carrier frequency based on the beamtracking.
 17. The method of claim 16, wherein the first carrierfrequency comprises a sub-6 gigahertz (GHz) band and the second carrierfrequency comprises a millimeter wave (mmW) band.
 18. The method ofclaim 16, wherein the first carrier frequency is associated with a firstradio access technology (RAT) and the second carrier frequency isassociated with a second RAT that is different from the first RAT. 19.The method of claim 16, wherein at least one second reference signal ofthe plurality of reference signals is received on at least one secondbeam of the plurality of beams based on the first indication of thefirst beam index.
 20. A method of wireless communication for a basestation, the method comprising: sending, to a user equipment (UE) in afirst carrier frequency, a message indicating an instruction to performbeam tracking between the base station and the UE in a second carrierfrequency that is different from the first carrier frequency;performing, based on the instruction, the beam tracking with the UE todetermine a communication beam, wherein the performing the beam trackingcomprises: sending a plurality of reference signals, wherein each of theplurality of reference signals is sent via a respective beam of aplurality of beams, and receiving, from the UE in the second carrierfrequency, information indicating at least one beam index correspondingto at least one beam of the plurality of beams based on a plurality ofmeasurements associated with receiving the plurality of referencesignals by the UE, wherein each measurement of the plurality ofmeasurements is associated with a respective beam of the plurality ofbeams; and communicating with the UE on the communication beam in thesecond carrier frequency based on the beam tracking.
 21. The method ofclaim 20, wherein the first carrier frequency comprises a sub-6gigahertz (GHz) band and the second carrier frequency comprises amillimeter wave (mmW) band.
 22. The method of claim 20, wherein thefirst carrier frequency is associated with a first radio accesstechnology (RAT) and the second carrier frequency is associated with asecond RAT that is different from the first RAT.
 23. The method of claim20, wherein at least one second reference signal of the plurality ofreference signals is sent on at least one second beam of the pluralityof beams based on the first indication of the first beam index.
 24. Anapparatus for wireless communication included in a user equipment (UE),the apparatus comprising: means for sending, to a base station in afirst carrier frequency, a request associated with performance of beamtracking between the base station and the UE in a second carrierfrequency that is different from the first carrier frequency; means forperforming, based on the request, the beam tracking with the basestation to determine a communication beam, wherein the means forperforming the beam tracking is configured for: receiving a plurality ofreference signals from the base station, wherein each of the pluralityof reference signals is received via a respective beam of a plurality ofbeams, and sending, to the base station in the second carrier frequency,information indicating at least one beam index corresponding to at leastone beam of the plurality of beams based on a plurality of measurementsassociated with receiving the plurality of reference signals, whereineach measurement of the plurality of measurements is associated with arespective beam of the plurality of beams; and means for communicatingwith the base station on the communication beam in the second carrierfrequency based on the beam tracking.
 25. The apparatus of claim 24,wherein the first carrier frequency comprises a sub-6 gigahertz (GHz)band and the second carrier frequency comprises a millimeter wave (mmW)band.
 26. The apparatus of claim 24, wherein the first carrier frequencyis associated with a first radio access technology (RAT) and the secondcarrier frequency is associated with a second RAT that is different fromthe first RAT.
 27. The apparatus of claim 24, wherein the requestindicates a beam index associated with the at least one first beam. 28.The apparatus of claim 27, wherein the request indicates the beam indexassociated with the at least one first beam based on one or moreresources associated with a random access channel (RACH).
 29. Theapparatus of claim 24, wherein at least one second reference signal ofthe plurality of reference signals is received on at least one secondbeam of the plurality of beams based on the first indication of thefirst beam index.
 30. The apparatus of claim 24, further comprising:means for detecting a radio link failure associated with communicationwith the base station on a serving beam in the second carrier frequency,wherein the means for sending the request is configured to send therequest based on the radio link failure.
 31. The apparatus of claim 30,wherein the means for detecting the radio link failure is configured to:measure a value associated with the serving beam, wherein the valuecomprises at least one of a signal-to-noise ratio (SNR), asignal-to-interference-plus-noise ratio (SINR), a received signalstrength indicator (RSSI), a reference signal received quality, or areference signal received power (RSRP); compare the value to athreshold; and detect the radio link failure based on the comparison ofthe value to the threshold.
 32. An apparatus for wireless communicationincluded in a base station, the apparatus comprising: means forreceiving, from a user equipment (UE) in a first carrier frequency, arequest associated with performance of beam tracking between the basestation and the UE in a second carrier frequency that is different fromthe first carrier frequency; means for performing, based on the request,the beam tracking with the UE to determine a communication beam, whereinthe means for performing the beam tracking is configured for: sending aplurality of reference signals, wherein each of the plurality ofreference signals is sent via a respective beam of a plurality of beams,and receiving, from the UE in the second carrier frequency, informationindicating at least one beam index corresponding to at least one beam ofthe plurality of beams based on a plurality of measurements associatedwith receiving the plurality of reference signals by the UE, whereineach measurement of the plurality of measurements is associated with arespective beam of the plurality of beams; and means for communicatingwith the UE on the communication beam in the second carrier frequencybased on the beam tracking.
 33. The apparatus of claim 32, wherein thefirst carrier frequency comprises a sub-6 gigahertz (GHz) band and thesecond carrier frequency comprises a millimeter wave (mmW) band.
 34. Theapparatus of claim 32, wherein the first carrier frequency is associatedwith a first radio access technology (RAT) and the second carrierfrequency is associated with a second RAT that is different from thefirst RAT.
 35. The apparatus of claim 32, wherein the request indicatesa beam index associated with the at least one first beam.
 36. Theapparatus of claim 35, wherein the request indicates the beam indexassociated with the at least one first beam based on one or moreresources associated with a random access channel (RACH).
 37. Theapparatus of claim 32, wherein at least one second reference signal ofthe plurality of reference signals is sent on at least one second beamof the plurality of beams based on the first indication of the firstbeam index.
 38. The apparatus of claim 32, wherein the request is basedon a radio link failure between the base station and the UE on a servingbeam.
 39. An apparatus for wireless communication included in a userequipment (UE), the apparatus comprising: means for receiving, from abase station in a first carrier frequency, a message indicating aninstruction to perform beam tracking between the base station and the UEin a second carrier frequency that is different from the first carrierfrequency; means for performing, based on the instruction, the beamtracking with the base station to determine a communication beam,wherein the means for performing the beam tracking is configured for:receiving a plurality of reference signals from the base station,wherein each of the plurality of reference signals is received via arespective beam of a plurality of beams, and sending, to the basestation in the second carrier frequency, information indicating at leastone beam index corresponding to at least one beam of the plurality ofbeams based on a plurality of measurements associated with receiving theplurality of reference signals, wherein each measurement of theplurality of measurements is associated with a respective beam of theplurality of beams; and means for communicating with the base station onthe communication beam in the second carrier frequency based on the beamtracking.
 40. The apparatus of claim 39, wherein the first carrierfrequency comprises a sub-6 gigahertz (GHz) band and the second carrierfrequency comprises a millimeter wave (mmW) band.
 41. The apparatus ofclaim 39, wherein the first carrier frequency is associated with a firstradio access technology (RAT) and the second carrier frequency isassociated with a second RAT that is different from the first RAT. 42.The apparatus of claim 39, wherein at least one second reference signalof the plurality of reference signals is received on at least one secondbeam of the plurality of beams based on the first indication of thefirst beam index.
 43. An apparatus for wireless communication includedin a base station, the apparatus comprising: means for sending, to auser equipment (UE) in a first carrier frequency, a message indicatingan instruction to perform beam tracking between the base station and theUE in a second carrier frequency that is different from the firstcarrier frequency; means for performing, based on the instruction, thebeam tracking with the UE to determine a communication beam, wherein themeans for performing the beam tracking is configured for: sending aplurality of reference signals, wherein each of the plurality ofreference signals is sent via a respective beam of a plurality of beams,and receiving, from the UE in the second carrier frequency, informationindicating at least one beam index corresponding to at least one beam ofthe plurality of beams based on a plurality of measurements associatedwith receiving the plurality of reference signals by the UE, whereineach measurement of the plurality of measurements is associated with arespective beam of the plurality of beams; and means for communicatingwith the UE on the communication beam in the second carrier frequencybased on the beam tracking.
 44. The apparatus of claim 43, wherein thefirst carrier frequency comprises a sub-6 gigahertz (GHz) band and thesecond carrier frequency comprises a millimeter wave (mmW) band.
 45. Theapparatus of claim 43, wherein the first carrier frequency is associatedwith a first radio access technology (RAT) and the second carrierfrequency is associated with a second RAT that is different from thefirst RAT.
 46. The apparatus of claim 43, wherein at least one secondreference signal of the plurality of reference signals is sent on atleast one second beam of the plurality of beams based on the firstindication of the first beam index.
 47. An apparatus for wirelesscommunication included in a user equipment (UE), the apparatuscomprising: a memory; and at least one processor coupled to the memoryand configured to: send, to a base station in a first carrier frequency,a request associated with performance of beam tracking between the basestation and the UE in a second carrier frequency that is different fromthe first carrier frequency; perform, based on the request, the beamtracking with the base station to determine a communication beam,wherein the performance of the beam tracking comprises to: receive aplurality of reference signals from the base station, wherein each ofthe plurality of reference signals is received via a respective beam ofa plurality of beams, and send, to the base station in the secondcarrier frequency, information indicating at least one beam indexcorresponding to at least one beam of the plurality of beams based on aplurality of measurements associated with receiving the plurality ofreference signals, wherein each measurement of the plurality ofmeasurements is associated with a respective beam of the plurality ofbeams; and communicate with the base station on the communication beamin the second carrier frequency based on the beam tracking.
 48. Theapparatus of claim 47, wherein the first carrier frequency comprises asub-6 gigahertz (GHz) band and the second carrier frequency comprises amillimeter wave (mmW) band.
 49. The apparatus of claim 47, wherein thefirst carrier frequency is associated with a first radio accesstechnology (RAT) and the second carrier frequency is associated with asecond RAT that is different from the first RAT.
 50. The apparatus ofclaim 47, wherein the request indicates a beam index associated with theat least one first beam.
 51. The apparatus of claim 50, wherein therequest indicates the beam index associated with the at least one firstbeam based on one or more resources associated with a random accesschannel (RACH).
 52. The apparatus of claim 47, wherein the at least oneprocessor is further configured to: detect a radio link failureassociated with communication with the base station on a serving beam inthe second carrier frequency, wherein the request is sent based on theradio link failure.
 53. The apparatus of claim 47, wherein the detectionof the radio link failure comprises to: measure a value associated withthe serving beam, wherein the value comprises at least one of asignal-to-noise ratio (SNR), a signal-to-interference-plus-noise ratio(SINR), a received signal strength indicator (RSSI), a reference signalreceived quality, or a reference signal received power (RSRP); comparethe value to a threshold; and detect the radio link failure based on thecomparison of the value to the threshold.
 54. An apparatus for wirelesscommunication included in a base station, the apparatus comprising: amemory; and at least one processor coupled to the memory and configuredto: receive, from a user equipment (UE) in a first carrier frequency, arequest associated with performance of beam tracking between the basestation and the UE in a second carrier frequency that is different fromthe first carrier frequency; perform, based on the request, the beamtracking with the UE to determine a communication beam, wherein theperformance of the beam tracking comprises to: send a plurality ofreference signals, wherein each of the plurality of reference signals issent via a respective beam of a plurality of beams, and receive, fromthe UE in the second carrier frequency, information indicating at leastone beam index corresponding to at least one beam of the plurality ofbeams based on a plurality of measurements associated with receiving theplurality of reference signals by the UE, wherein each measurement ofthe plurality of measurements is associated with a respective beam ofthe plurality of beams; and communicate with the UE on the communicationbeam in the second carrier frequency based on the beam tracking.
 55. Theapparatus of claim 54, wherein the first carrier frequency comprises asub-6 gigahertz (GHz) band and the second carrier frequency comprises amillimeter wave (mmW) band.
 56. The apparatus of claim 54, wherein thefirst carrier frequency is associated with a first radio accesstechnology (RAT) and the second carrier frequency is associated with asecond RAT that is different from the first RAT.
 57. The apparatus ofclaim 54, wherein the request indicates a beam index associated with theat least one first beam.
 58. The apparatus of claim 57, wherein therequest indicates the beam index associated with the at least one firstbeam based on one or more resources associated with a random accesschannel (RACH).
 59. The apparatus of claim 54, wherein the request isbased on a radio link failure between the base station and the UE on aserving beam.
 60. An apparatus for wireless communication included in auser equipment (UE), the apparatus comprising: a memory; and at leastone processor coupled to the memory and configured to: receive, from abase station in a first carrier frequency, a message indicating aninstruction to perform beam tracking between the base station and the UEin a second carrier frequency that is different from the first carrierfrequency; perform, based on the instruction, the beam tracking with thebase station to determine a communication beam, wherein the performanceof the beam tracking comprises to: receive a plurality of referencesignals from the base station, wherein each of the plurality ofreference signals is received via a respective beam of a plurality ofbeams, and send, to the base station in the second carrier frequency,information indicating at least one beam index corresponding to at leastone beam of the plurality of beams based on a plurality of measurementsassociated with receiving the plurality of reference signals, whereineach measurement of the plurality of measurements is associated with arespective beam of the plurality of beams; and communicate with the basestation on the communication beam in the second carrier frequency basedon the beam tracking.
 61. The apparatus of claim 60, wherein the firstcarrier frequency comprises a sub-6 gigahertz (GHz) band and the secondcarrier frequency comprises a millimeter wave (mmW) band.
 62. Theapparatus of claim 60, wherein the first carrier frequency is associatedwith a first radio access technology (RAT) and the second carrierfrequency is associated with a second RAT that is different from thefirst RAT.
 63. An apparatus for wireless communication included in abase station, the apparatus comprising: a memory; and at least oneprocessor coupled to the memory and configured to: send, to a userequipment (UE) in a first carrier frequency, a message indicating aninstruction to perform beam tracking between the base station and the UEin a second carrier frequency that is different from the first carrierfrequency; perform, based on the instruction, the beam tracking with theUE to determine a communication beam, wherein the performance of thebeam tracking comprises to: send a plurality of reference signals,wherein each of the plurality of reference signals is sent via arespective beam of a plurality of beams, and receive, from the UE in thesecond carrier frequency, information indicating at least one beam indexcorresponding to at least one beam of the plurality of beams based on aplurality of measurements associated with receiving the plurality ofreference signals by the UE, wherein each measurement of the pluralityof measurements is associated with a respective beam of the plurality ofbeams; and communicate with the UE on the communication beam in thesecond carrier frequency based on the beam tracking.
 64. The apparatusof claim 63, wherein the first carrier frequency comprises a sub-6gigahertz (GHz) band and the second carrier frequency comprises amillimeter wave (mmW) band.
 65. The apparatus of claim 63, wherein thefirst carrier frequency is associated with a first radio accesstechnology (RAT) and the second carrier frequency is associated with asecond RAT that is different from the first RAT.
 66. A non-transitory,computer-readable medium storing computer-executable code for wirelesscommunication by a user equipment (UE), comprising code to: send, to abase station in a first carrier frequency, a request associated withperformance of beam tracking between the base station and the UE in asecond carrier frequency that is different from the first carrierfrequency; perform, based on the request, the beam tracking with thebase station to determine a communication beam, wherein the performanceof the beam tracking comprises to: receive a plurality of referencesignals from the base station, wherein each of the plurality ofreference signals is received via a respective beam of a plurality ofbeams, and send, to the base station in the second carrier frequency,information indicating at least one beam index corresponding to at leastone beam of the plurality of beams based on a plurality of measurementsassociated with receiving the plurality of reference signals, whereineach measurement of the plurality of measurements is associated with arespective beam of the plurality of beams; and communicate with the basestation on the communication beam in the second carrier frequency basedon the beam tracking.
 67. A non-transitory, computer-readable mediumstoring computer-executable code for wireless communication by a basestation, comprising code to: receive, from a user equipment (UE) in afirst carrier frequency, a request associated with performance of beamtracking between the base station and the UE in a second carrierfrequency that is different from the first carrier frequency; perform,based on the request, the beam tracking with the UE to determine acommunication beam, wherein the performance of the beam trackingcomprises to: send a plurality of reference signals, wherein each of theplurality of reference signals is sent via a respective beam of aplurality of beams, and receive, from the UE in the second carrierfrequency, information indicating at least one beam index correspondingto at least one beam of the plurality of beams based on a plurality ofmeasurements associated with receiving the plurality of referencesignals by the UE, wherein each measurement of the plurality ofmeasurements is associated with a respective beam of the plurality ofbeams; and communicate with the UE on the communication beam in thesecond carrier frequency based on the beam tracking.
 68. Anon-transitory, computer-readable medium storing computer-executablecode for wireless communication by a user equipment (UE), comprisingcode to: receive, from a base station in a first carrier frequency, amessage indicating an instruction to perform beam tracking between thebase station and the UE in a second carrier frequency that is differentfrom the first carrier frequency; perform, based on the instruction, thebeam tracking with the base station to determine a communication beam,wherein the performance of the beam tracking comprises to: receive aplurality of reference signals from the base station, wherein each ofthe plurality of reference signals is received via a respective beam ofa plurality of beams, and send, to the base station in the secondcarrier frequency, information indicating at least one beam indexcorresponding to at least one beam of the plurality of beams based on aplurality of measurements associated with receiving the plurality ofreference signals, wherein each measurement of the plurality ofmeasurements is associated with a respective beam of the plurality ofbeams; and communicate with the base station on the communication beamin the second carrier frequency based on the beam tracking.
 69. Anon-transitory, computer-readable medium storing computer-executablecode for wireless communication by a base station, comprising code to:send, to a user equipment (UE) in a first carrier frequency, a messageindicating an instruction to perform beam tracking between the basestation and the UE in a second carrier frequency that is different fromthe first carrier frequency; perform, based on the instruction, the beamtracking with the UE to determine a communication beam, wherein theperformance of the beam tracking comprises to: send a plurality ofreference signals, wherein each of the plurality of reference signals issent via a respective beam of a plurality of beams, and receive, fromthe UE in the second carrier frequency, information indicating at leastone beam index corresponding to at least one beam of the plurality ofbeams based on a plurality of measurements associated with receiving theplurality of reference signals by the UE, wherein each measurement ofthe plurality of measurements is associated with a respective beam ofthe plurality of beams; and communicate with the UE on the communicationbeam in the second carrier frequency based on the beam tracking.